Welcome to CLUE++’s documentation!¶

CLUE++ is a light-weight extensions to the C++ standard library. It provides a collection of components that are widely useful in practical development. These components include a subset of functions and classes introduced in C++14 or later technical specifications (but are also useful for C++11), and some new facilities that we feel are useful in practice.

All components provided by this library are implemented in a way that closely follow the convention of the standard library. In particular, for those components that are backported from C++14 or new technical specifications, we strictly follow the standard specification whenever possible (with in the capability of C++11).

Contents:¶

Basic utilites¶

Optional (Nullable)¶

In the C++ Extensions for Library Fundamentals (N4480), a class template optional is introduced, which represents objects that may possibly contain a value. Such types are widely provided by modern programming languages (e.g. Nullable in C#, Maybe in Haskell, Optional in Swift, and Option in Rust), and have shown their important utility in practice. This library “backports” the optional type to C++11 (within the namespace clue).

Here is a simple example that illustrates the use of the optional class.

#include <cmath>
#include <clue/optional.hpp>

using namespace clue;

inline optional<double> safe_sqrt(double x) {
    return x >= 0.0 ?
        make_optional(std::sqrt(x)) :
        optional<double>();
}

auto u = safe_sqrt(-1.0);  // -> optional<double>()
(bool)u;          // -> false
u.value();        // throws an exception
u.value_or(0.0);  // -> 0.0

auto v = safe_sqrt(4.0);  // -> optional<double>(2.0)
(bool)v;          // -> true
v.value();        // -> 2.0
v.value_or(0.0);  // -> 2.0

The standard documentation of the optional type is available here. Below is a brief description of this type.

Types¶

The class template optional is declared as:

class optional¶

Formal:

template <typename T>
class optional;

Parameters:	T – The type of the (possibly) contained value.

The class optional<T> has a member typedef value_type defined as T.

In addition, several helper types are provided:

class in_place_t¶: A tag type to indicate in-place construction of an optional object. It has a predefined instance in_place.

class nullopt_t¶: A tag type to indicate an optional object with uninitialized state. It is a predefined instance nullopt.

Constructors¶

An optional object can be constructd in different ways:

constexpr optional()¶: Constructs an empty optional object, which does not contain a value.

constexpr optional(nullopt_t)¶: Constructs an empty optional object (equivalent to optional<T>()).

optional(const optional&)¶: Copy constructor, with default behavior.

optional(optional&&)¶: Move constructor, with default behavior.

constexpr optional(const value_type &v)¶: Construct an optional object that contains (a copy of) the input value v.

constexpr optional(value_type &&v)¶: Construct an optional object that contains the input value v (moved in).

constexpr optional(in_place_t, Args&&... args)¶: Construct an optional object, with the contained value constructed inplace with the initializing arguments args.

Modifiers¶

After an optional object is constructed, its value can be re-constructed later using swap, emplace, or the assignment operator.

void swap(optional &other)¶: Swap with another optional object other.

void emplace(Args&&... args)¶: Re-construct the contained value using the provided arguments args.

Observers¶

Note

This class provides operator-> to allow the access of the contained vlaue in a pointer form, and operator* to allow the access in a dereferenced form. One must use these operators when the optional object actually contains a value, otherwise it is undefined behavior.

A safer (but slightly less efficient) way to access the contained value is to use value or value_or member functions described below.

explicit constexpr operator bool() const noexcept¶

Convert the object to a boolean value.

Returns:	`true` when the object contains a value, or `false` otherwise.

constexpr value_type const &value() const¶

Get a const reference to the contained value.

Throw:	an exception of class `bad_optional_access` when the object is empty.

value_type &value()¶

Get a reference to the contained value.

Throw:	an exception of class `bad_optional_access` when the object is empty.

constexpr value_type value_or(U &&v) const &¶: Get the contained value, or a static convertion of v to the type T (when the object is empty).

value_type value_or(U &&v) &&¶: Get the contained value, or a static convertion of v to the type T (when the object is empty).

Non-member Functions¶

void swap(optional<T> &x, optional<T> &y)¶: Swap two optional objects x and y. Equivalent to x.swap(y).

constexpr optional<R> make_optional(T &&v)¶

Make an optional object that encapsulates a value v.

Returns:	An optional object of class `optional<R>`, where the template parameter `R` is defined as `typename std::decay<T>::type`.

Comparison¶

Comparison operators ==, !=, <, >, <=, >= are provided to compare optional objects.

Two optional objects are considered as equal if they meet either of the following two conditions:

they are both empty, or
they both contain values, and the contained values are equal.

An optional object x are considered as lesss than another optional object y, if either of the following conditions are met:

x is empty while y is not.
they both contain values, and x.value() < y.value().

Note

Comparison between an optional object and a value v of type T is allowed. In such cases, v is treated as an optional object that contains a value v, and then the rules above apply.

Timing¶

Timing, namely to measure the run-time of a piece of code, is a common practice in development, especially in contexts where performance is critical (e.g. numerical computation). CLUE++ provides timing facilities to facilitate this practice. All these facilities are in the namespace clue.

Representation of duration¶

A class duration is introduced to represent time durations.

class duration¶: A wrapper of std::chrono::high_resolution_clock::duration that exposes more user friendly interface to work with duration.

The stop_watch class use a duration object to represent the elapsed time. The duration class has several member functions to retrieve the duration in different units.

explicit constexpr duration() noexcept¶: Construct a zero duration.

constexpr duration(const value_type &val) noexcept¶: Construct a duration with an object of class value_type, namely std::chrono::high_resolution_clock::duration.

constexpr double get() const noexcept¶

dur.get<U>() gets the duration in unit U. Here, U should be an instantiation of the class template std::ratio.

The following table lists the correspondence between U and physical time units.

type `U`	physical unit
`std::ratio<1>`	seconds
`std::milli`	milliseconds
`std::micro`	microseconds
`std::nano`	nanoseconds
`std::ratio<60>`	minutes
`std::ratio<3600>`	hours

A set of convenient member functions are also provided to make this a bit easier:

constexpr double secs() const noexcept¶: Get the duration in seconds.

constexpr double msecs() const noexcept¶: Get the duration in milliseconds.

constexpr double usecs() const noexcept¶: Get the duration in microseconds.

constexpr double nsecs() const noexcept¶: Get the duration in nanoseconds.

constexpr double mins() const noexcept¶: Get the duration in minutes.

constexpr double hours() const noexcept¶: Get the duration in minutes.

Stopwatch¶

A stop_watch class is introduced to measure running time.

class stop_watch¶

Stop watch class for measuring run-time, in wall-clock sense.

Note:	Internally, it relies on the class `std::chrono::high_resolution_clock` introduced in C++11 for timing, and hence it is highly portable.

The class stop_watch has the following members:

explicit stop_watch(bool st = false) noexcept¶: Construct a stop watch. By default, it is not started. One can set st to true to let the stop watch starts upon construction.

void reset() noexcept¶: Reset the watch: stop it and clear the accumulated elapsed duration.

void start() noexcept¶: Start or resume the watch.

void stop() noexcept¶: Stop the watch and accumulates the duration of last run to the total elapsed duration.

duration elapsed() const noexcept¶: Get the total elapsed time.

Here is an example to illustrate the use of the stop_watch class.

#include <clue/timing.hpp>

using namespace clue;

// simple use

stop_watch sw(true);  // starts upon construction
run_my_code();
std::cout << sw.elapsed().secs() << std::endl;

// multiple laps

stop_watch sw1;
for (size_t i = 0; i < 10; ++i) {
    sw1.start();
    run_my_code();
    sw1.stop();
    std::cout << "cumulative elapsed = "
              << sw1.elapsed().secs() << std::endl;
}

Timing functions¶

We also provide convenient functions to help people time a certain function.

duration simple_time(F &&f, size_t n, size_t n0 = 0)¶

Run the function f() for n times and return the total elapsed duration.

Parameters:	f – The function to be timed. n – The number of times `f` is to be executed. n0 – The number of pre-running times. If `n0 > 0`, it will pre-run `f` for `n0` times to warm up the function (for certain functions, the first run or first several runs may take substantially longer time).

calibrated_timing_result calibrated_time(F &&f, double measure_secs = 1.0, double calib_secs = 1.0e-4)¶

Calibrated timing.

This function may spend a little bit time (around calib_secs seconds) to roughly measure the average running time of f() (i.e. calibaration), and then run f() for more times for actual measurement such that the entire duration of measurement is around measure_secs seconds.

Parameters:	f – The function to be timed. measure_secs – The time to be spent on actual measurement (in seconds). calib_secs – The time to be spent on calibration (in seconds).
Returns:	the timing result of class `calibrated_timing_result`.

class calibrated_timing_result¶

A struct to represent the result of calibrated timing, which has two fields:

count_runs: the number of runs in actual timing.
elapsed_secs: elapsed duration of the actual timing process, in seconds.

Examples:

// source file: examples/ex_timing.hpp

#include <clue/timing.hpp>
#include <cstdio>
#include <cstring>

using namespace clue;

static char src[1000000];
static char dst[1000000];

void unused(char c) {}

// copy 1 million bytes
void copy1M() {
    std::memcpy(dst, src, sizeof(src));

    // ensure the copy actually happens in optimized code
    volatile char v = dst[0];
    unused(v);   // suppress unused warning
}

int main() {
    std::memset(src, 0, sizeof(src));

    auto r = calibrated_time(copy1M);

    std::printf("Result:\n");
    std::printf("    runs    = %zu\n", r.count_runs);
    std::printf("    elapsed = %.4f secs\n", r.elapsed_secs);

    double gps = r.count_runs * 1.0e-3 / r.elapsed_secs;
    std::printf("    speed   = %.4f Gbytes/sec\n", gps);

    return 0;
}

Value Range¶

It is a very common pattern in C/C++ programming to write loops that enumerate values within a certain range, such as

for (int i = 0; i < n; ++i) {
    // do something
}

In C++11, the range for-loop syntax is introduced, which allow concise expression of the looping over elements in a container. However, one has to resort to the old pattern when enumerating values. Here, we provide a class template value_range that wraps a range of values to a light-weight container-like object. Below is an example:

#include <clue/value_range.hpp>

using namespace clue;

size_t n = 10

// enumerate i from 0 to n-1
for (size_t i: vrange(n)) {
    // do something on i
}

double a = 2.0, b = 9.0;
// enumerate v from 2.0 to 8.0
for (auto v: vrange(a, b)) {
    // do something on i
}

std::vector<int> a{1, 2, 3, 4, 5};
std::vector<int> b{5, 6, 7, 8, 9};
std::vector<int> r

// enumrate i from 0 to a.size() - 1
for (auto i: indices(a)) {
    r.push_back(a[i] + b[i]);
}

Documentation of value_range and relevant functions are given below.

The `value_range` and `stepped_value_range` class templates¶

Formally, the class template value_range is defined as:

class value_range¶

Formal:

template<typename T,
         typename D=typename default_difference<T>::type,
         typename Traits=value_range_traits<T, D>>
class value_range;

Classes to represent continuous value ranges, such as 1, 2, 3, 4, ....

Parameters:

T – The value type.
D – The difference type. This can be omitted, and it will be, by default, set to default_difference<T>::type.
Traits – A traits class that specifies the behavior of the value type T. This class has to satisfy the EnumerableValueTraits concept, which will be explained in the section enumerable_value_traits. In general, one may omit this, and it will be, by default, set to value_type_traits<T, D>.

class default_difference¶

default_difference<T> provides a member typedef that indicates the default difference type for T.

In particular, if T is an unsigned integer type, default_difference<T>::type is std::make_signed<T>::type. In other cases, default_difference<T>::type is identical to T.

To enumerate non-numerical types (e.g. dates), one should specialize default_difference<T> to provide a suitable difference type.

class stepped_value_range¶

Formal:

template<typename T,
         typename S,
         typename D=typename default_difference<T>::type,
         typename Traits=value_range_traits<T, D>>
class stepped_value_range;

Classes to represent stepped ranges, such as 1, 3, 5, 7, ....

Parameters:	T – The value type. S – The step type. D – The difference type. By default, it is `default_difference_type<T>::type`. Traits – The trait class for `T`. By default, it is `value_type_traits<T, D>`.

Note

For stepped_value_range<T, S>, only unsigned integral types for T and S are supported at this point.

Member types¶

The class value_range<T> or stepped_value_range<T, S> contains a series of member typedefs as follows:

types	definitions
`value_type`	`T`
`difference_type`	`D`
`step_type`	`S`
`traits_type`	`Traits`
`size_type`	`std::size_t`
`pointer`	`const T*`
`const_pointer`	`const T*`
`reference`	`const T&`
`const_reference`	`const T&`
`iterator`	implementing `RandomAccessIterator`
`const_iterator`	`iterator`

Note

For value_range<T>, the step_type is the same as size_type.

Construction¶

The value_range<T> and stepped_value_range<T, S> classes have simple constructors.

constexpr value_range(const T &vbegin, const T &vend)¶

Parameters:	vbegin – The beginning value (inclusive). vend – The ending value (exclusive).

For example, value_range(0, 3) indicates the following sequence 0, 1, 2.

stepped_value_range(const T &vbegin, const T &vend, const S &step)¶

Parameters:	vbegin – The beginning value (inclusive). vend – The ending value (exclusive). step – The incremental step.

For example, stepped_value_range(0, 2, 5) indicates the following sequence 0, 2, 4.

Note

These classes also have a copy constructor, an assignment operator, a destructor and a swap member function, all with default behaviors.

Note

For stepped ranges, the step must be positive. Zero or negative step would result in undefined behavior. The size of a stepped range is computed as (e - b + (s - 1)) / s.

In addition, convenient constructing functions are provided, with which the user does not need to explictly specify the value type (which would be infered from the arguments):

constexpr value_range<T> vrange(const T &u)¶: Equivalent to value_range<T>(static_cast<T>(0), u).

constexpr value_range<T> vrange(const T &a, const T &b)¶: Equivalent to value_range<T>(a, b).

value_range<Siz> indices(const Container &c)¶: Returns a value range that contains indices from 0 to c.size() - 1. Here, the value type Siz is Container::size_type.

Properties and element access¶

The value_range<T> and stepped_value_range<T, S> classes provide a similar set of member functions that allow access of the basic properties and individual values in the range, as follows.

constexpr size_type size() const noexcept¶: Get the size of the range, i.e. the number of values contained in the range.

constexpr bool empty() const noexcept¶: Get whether the range is empty, i.e. contains no values.

constexpr size_type step() const noexcept¶

Get the step size.

Note:	For `value_range<T>`, the step size is always `1`.

constexpr T front() const noexcept¶: Get the first value within the range.

constexpr T back() const noexcept¶: Get the last value within the range.

constexpr T begin_value() const noexcept¶: Get the first value in the range (equivalent to front()).

constexpr T end_value() const noexcept¶: Get the value that specifies the end of the value, which is the value next to back().

constexpr T operator[](size_type pos) const¶: Get the value at position pos, withou bounds checking.

constexpr T at(size_type pos) const¶

Get the value at position pos, with bounds checking.

Throw:	an exception of class `std::out_of_range` if `pos >= size()`.

Iterators¶

constexpr const_iterator cbegin() const¶: Get a const iterator to the beginning.

constexpr const_iterator cend() const¶: Get a const iterator to the end.

constexpr iterator begin() const¶: Get a const iterator to the beginning, equivalent to cbegin().

constexpr iterator end() const¶: Get a const iterator to the end, equivalent to cend().

Note

A value range or stepped value range does not actually store the values in the range. Hence, the iterators are proxies that do not refer to an existing location in memory. Instead, *iter returns the value itself instead of a reference. In spite of this subtle difference from a typical iterator, we find that it works perfectly with most STL algorithms.

The EnumerableValueTraits concept¶

The class template value_range has a type parameter Traits, which has to satisfy the following concept.

// x, y are values of type T, and n is a value of type D

Traits::increment(x);       // in-place increment of x
Traits::decrement(x);       // in-place decrement of x
Traits::increment(x, n);    // in-place increment of x by n units
Traits::decrement(x, n);    // in-place decrement of x by n units

Traits::next(x);        // return the value next to x
Traits::prev(x);        // return the value that precedes x
Traits::next(x, n);     // return the value ahead of x by n units
Traits::prev(x, n);     // return the value behind x by n units

Traits::eq(x, y);       // whether x is equal to y
Traits::lt(x, y);       // whether x is less than y
Traits::le(x, y);       // whether x is less than or equal to y

Traits::difference(x, y); // the difference between x and y, i.e. x - y

By default, the builtin value_range_traits<T, D> would be used and users don’t have to specify the traits explicitly. However, one can specify a different trait class to provide special behaviors.

Predicates¶

CLUE++ provides a series of higher-order functions for generating predicates (functors that returns bool), in the header <clue/predicates.hpp>. These predicates can be very useful in programming for expressing certain conditions.

Take a look of the following example, where we want to determine whether all elements are positive. With C++11, this can be accomplished as:

std::all_of(s.begin(), s.end(), [](int x){ return x > 0; });

This is convenient enough. However, still expressing simple conditions like positiveness using a full-fledged lambda expression remains cumbersome, especially when there are many conditions to express. CLUE provides a higher-order function gt, with which [](int x){ return x > 0; } above can be simplified as gt(0), and consequently the code above can be rewritten as:

std::all_of(s.begin(), s.end(), gt(0));

Generic predicates¶

The following table lists the predicates provided by CLUE. Let x be the value to be tested by the predicates. Note that all these predicates are in the namespace clue.

functors	conditions
`eq(v)`	`x == v`
`ne(v)`	`x != v`
`gt(v)`	`x > v`
`ge(v)`	`x >= v`
`lt(v)`	`x < v`
`le(v)`	`x <= v`
`in(s)`	`x` is in `s`, i.e. `x` is equal to one of the elements of `s`
`in_range(l, r)`	`x >= l && x <= r`

Note

For in(s), s can be a C-string. In this case, the generated predicate returns true, when the input character x equals one of the character in s.

CLUE also provides and_ and or_ to combine conditions.

and_(p1, p2, ...)¶

Return a predicate, which returns true for an argument x when p1(x) && p2(x) && ....

Example: To express the condition like a < x < b, one can write and_(gt(a), lt(b)), or if it is a closed interval as a <= x <= b, then one can write and_(ge(a), le(b)).

or_(p1, p2, ...)¶

Return a predicate, which returns true for an argument x when p1(x) || p2(x) || ....

Example: or_(eq(a), eq(b), eq(c)) expresses the condition that x is equal to either a, b, or c.

Char predicates¶

CLUE provides several predicates for testing characters (of type char or wchar_t) within the namespace clue::chars, as follows. These functors can be very useful in text parsing.

functors	conditions
`chars::is_space`	`std::isspace(x)`
`chars::is_blank`	`std::isblank(x)`
`chars::is_digit`	`std::isdigit(x)`
`chars::is_xdigit`	`std::isxdigit(x)`
`chars::is_alpha`	`std::isalpha(x)`
`chars::is_alnum`	`std::isalnum(x)`
`chars::is_punct`	`std::ispunct(x)`
`chars::is_upper`	`std::isupper(x)`
`chars::is_lower`	`std::islower(x)`

Note

All these is_space etc are typed functors. Unlike the C-function such as isspace, these functors are likely to be inlined when passed to higher-level algorithms (e.g. std::all_of, std::find, etc). Also these functors work with both char and wchar_t. For example, char::is_space(c) calls std::iswspace internally when c is of type wchar_t.

Float predicates¶

CLUE also provides predicates for testing floating point numbers, within the namespace clue::floats.

functors	conditions
`floats::is_finite`	`std::isfinite(x)`
`floats::is_inf`	`std::isinf(x)`
`floats::is_nan`	`std::isnan(x)`

Note

These functors work with float, double, and long double.

(Demangled) Type Names¶

CLUE provides facilities to obtain (demangled) names of C++ types. All following functions are in the header <clue/type_name.hpp>, and they are in the namespace clue.

bool has_demangle()¶: Whether CLUE provides demangling support.

Note

At this point, demangling is supported with GCC, Clang, and ICC.

std::string type_name()¶: typename<T>() returns a (demangled) name of type T.

Note

It returns the demangled name when has_demangle(), otherwise it returns the name as given by typeid(T).name().

std::string type_name(x)¶: Returns the (demangled) name of the type of x.

std::string demangle(const char *name)¶: Demangles the input name (the one returned by typeid(T).name()).

Note

When has_demangle() is true, namely, CLUE has demangling support, this returns the demangled name, otherwise it returns a string capturing the intput name.

Miscellaneous Utilities¶

CLUE also provides some utilities that are handy in programming practice. These utilities are provided by the header <clue/misc.hpp>.

make_unique(args...)¶

make_unique<T>(args...) constructs an object of type T and wraps it in a unique pointer of class std::unique_ptr<T>.

Here, args are the arguments to be forwarded to the constructor.

It is equivalent to unique_ptr<T>(new T(std::forward<Args>(args)...)).

pass(args...)¶

Accepts arbitrary arguments and does nothing.

The purpose of this function is mainly to trigger the execution of all the argument expressions in a variadic context.

class temporary_buffer¶

Formal:

template<typename T>
class temporary_buffer

Tempoary buffer.

An object of this class invokes std::get_temporary_buffer on construction, and std::return_temporary_buffer on destruction.

Note

A temporary buffer is supposed to be used locally, and it is not copyable or movable.

Examples:

#include <clue/misc.hpp>

void myfun(size_t n) {
    // calls std::get_temporary_buffer to acquire a buffer
    // that can host at least n integers.
    temporary_buffer<int> buf(n);

    size_t cap = buf.capacity();  // get the size that are actually allocated
    int *p = buf.data();  // get the memory address

    // do somthing with buf ...

    // upon exit, the buffer will be returned by calling
    // std::return_temporary_buffer
}

Containers and Views¶

Array View¶

An array view is a light-weight container-like wrapper of a pointer and a size. It provides a convenient way to turn a contiguous memory region into a container-like object. In practice, such an object maintains the efficiency of a raw pointer while providing richer API to work with memory regions. Below is an example to illustrate this.

#include <clue/array_view.hpp>

using namespace clue;

int a[] = {1, 2, 3, 4, 5};

for (int& v: aview(a, 5)) {
    std::cout << v << std::endl;
    v += 1;
}

In practice, it is not uncommon that you maintain a vector in your object and would like to expose the elements to the users (without allowing the users to refer to the vector directly). In such cases, it would be a good idea to return an array view.

using namespace clue;

class A {
public:
    // ...

    array_view<const T> elements() const {
        return aview(elems_.data(), elems_.size());
    }

private:
    std::vector<T> elems_;
};

// client code

A a( /* ... */ );

std::cout << "# elems = " << a.elements().size() << std::endl;
for (const T& v: a.elements()) {
    std::cout << v << std::endl;
}

The `array_view` class template¶

class array_view¶

Formal:

template<typename T>
class array_view;

Parameters:	T – The element type.

Note

In general, array_view<T> allows modification of the elements, e.g a[i] = x. To provide a readonly view, one can use array_view<const T>.

Member types¶

The class array_view<T> contains a series of member typedefs as follows:

types	definitions
`value_type`	`std::remove_cv<T>::type`
`size_type`	`std::size_t`
`difference_type`	`std::ptrdiff_t`
`pointer`	`T*`
`const_pointer`	`const T*`
`reference`	`T&`
`const_reference`	`const T&`
`iterator`	implementing `RandomAccessIterator`
`const_iterator`	`iterator`
`reverse_iterator`	`std::reverse_iterator<iterator>`
`const_reverse_iterator`	`std::reverse_iterator<const_iterator>`

Construction¶

constexpr array_view() noexcept¶: Construct an empty view, with null data pointer.

constexpr array_view(pointer data, size_type len) noexcept¶: Construct an array view, with data pointer data and size len.

Note

It also has a copy constructor, an assignment operator, a destructor and a swap member function, all with default behaviors. It is worth noting that the copy construction/assignment of a view is shallow, meaning that only the pointer and the size value are copied, the underlying content remains there.

A convenient function aview is provided for constructing array views without the need of explicitly articulating the value type.

constexpr array_view<T> aview(T *p, size_t n) noexcept¶

Construct an array view, with data pointer p and size n.

Note:	If `p` is of type `T`, it returns a view of class `array_view<T>`, and if `p` is a const pointer of type `const T`, it returns a view of class `array_view<const T>`, which is a read-only view.

Basic properties and element access¶

constexpr size_type size() const noexcept¶: Get the size of the range, i.e. the number of elements referred to by the view.

constexpr bool empty() const noexcept¶: Get whether the view is empty, i.e. refers to no elements.

constexpr const_pointer data() const noexcept¶: Get a const pointer to the base address.

pointer data() noexcept¶: Get a pointer to the base address.

constexpr const_reference front() const¶: Get a const reference to the first element within the view.

reference front()¶: Get a reference to the first element within the view.

constexpr const_reference back() const¶: Get a const reference to the last element within the view.

reference back()¶: Get a reference to the last element within the view.

constexpr const_reference operator[](size_type pos) const¶: Get a const reference to the element at position pos, without bounds checking.

reference operator[](size_type pos)¶: Get a reference to the element at position pos, without bounds checking.

constexpr const_reference at(size_type pos) const¶

Get a const reference to the element at position pos, with bounds checking.

Throw:	an exception of class `std::out_of_range` if `pos >= size()`.

reference at(size_type pos)¶

Get a reference to the element at position pos, with bounds checking.

Throw:	an exception of class `std::out_of_range` if `pos >= size()`.

Iterators¶

constexpr const_iterator cbegin() const¶: Get a const iterator to the beginning.

constexpr const_iterator cend() const¶: Get a const iterator to the end.

constexpr const_iterator begin() const¶: Get a const iterator to the beginning, equivalent to cbegin().

constexpr const_iterator end() const¶: Get a const iterator to the end, equivalent to cend().

iterator begin()¶: Get an iterator to the beginning.

iterator end()¶: Get an iterator to the end.

constexpr const_iterator crbegin() const¶: Get a const reverse iterator to the reversed beginning.

constexpr const_iterator crend() const¶: Get a const reverse iterator to the reversed end.

constexpr iterator rbegin() const¶: Get a const reverse iterator to the reversed beginning, equivalent to crbegin().

constexpr iterator rend() const¶: Get a const reverse iterator to the reversed end, equivalent to crend().

iterator rbegin()¶: Get a reverse iterator to the reversed beginning.

iterator rend()¶: Get a reverse iterator to the reversed end.

Reindexed View¶

In practice, people often want to work on a selected subset of elements of a sequence. A typical approach is to copy those elements to another container, as

std::vector<int> source{1, 2, 3, 4, 5, 6};
std::vector<size_t> selected_inds{5, 1, 4};

std::vector<int> selected;
selected.reserve(selected_inds.size());
for (size_t i: selected_inds) {
    selected.push_back(source[i]);
}

This approach is cumbersome and inefficient. CLUE++ introduces a class template reindexed_view to tackle this problem. An reindexed view is an object that refers to the selected elements while providing container-like API to work with them. Below is an example:

#include <clue/reindexed_view.hpp>

using namespace clue;

std::vector<int> source{1, 2, 3, 4, 5, 6};
std::vector<size_t> selected_inds{5, 1, 4};

for (auto v: reindexed(source, selected_inds)) {
    // do something on v
}

Below is the documentation of this class template and relevant functions.

The `reindexed_view` class template¶

class reindexed_view¶

Formal:

template<class Container, class Indices>
class reindexed_view;

Parameters:	Container – The type of the element container. Indices – The type of the indices container.

Both Container and Indices need to be random access containers.

Note

Here, the Container type can be a const type, e.g. const vector<int>. Using a constant container type as the template argument would lead to a read-only view, which are often very useful.

Member types¶

The class reindexed_view<Container, Indices> contains a series of member typedefs as follows:

types	definitions
`container_type`	`std::remove_cv<Container>::type`
`indices_type`	`std::remove_cv<Indices>::type`
`value_type`	`container_type::value_type`
`size_type`	`indices_type::size_type`
`difference_type`	`indices_type::difference_type`
`const_reference`	`container_type::const_reference`
`const_pointer`	`container_type::const_pointer`
`const_iterator`	`container_type::const_iterator`

There are also other member typedefs, whose definitions depend on the constness of Container.

type reference¶: Defined as container_type::const_reference when Container is a const type, or container_type::reference otherwise.

type pointer¶: Defined as container_type::const_pointer when Container is a const type, or container_type::pointer otherwise.

type iterator¶: Defined as container_type::const_iterator when Container is a const type, or container_type::iterator otherwise.

Construction¶

constexpr reindexed_view(Container &container, Indices &indices) noexcept¶: Construct a reindexed view, with the given source container and index sequence.

Note

A reindexed view only maintains references to container and indices. It is the caller’s responsibility to ensure that the container and indices remain valid while using the view. Otherwise, undefined behaviors may result.

A convenient function reindexed is provided for creating reindexed views, without requiring the user to explicitly specify the container type and the indices type:

constexpr reindexed_view<Container, Indices> reindexed(Container &c, Indices &inds)¶

Construct a reindexed view, with the given source container and index sequence, where the types Container and Indices are deduced from arguments.

Note:	If `c` is a const reference, then `Container` will be deduced to a const type. The same also applies to `indices`.

Basic properties and element access¶

constexpr bool empty() const noexcept¶: Get whether the view is empty (i.e. contains no selected elements). It is equal to indices.empty().

constexpr size_type size() const noexcept¶: Get the number of selected elements. It is equal to indices.size().

constexpr size_type max_size() const noexcept¶: Get the maximum number of elements that a view can possibly refer to.

constexpr const_reference front() const¶: Get a const reference to the first element within the view.

reference front()¶: Get a reference to the first element within the view.

constexpr const_reference back() const¶: Get a const reference to the last element within the view.

reference back()¶: Get a reference to the last element within the view.

constexpr const_reference operator[](size_type pos) const¶: Get a const reference to the element at position pos, without bounds checking.

reference operator[](size_type pos)¶: Get a reference to the element at position pos, without bounds checking.

constexpr const_reference at(size_type pos) const¶: Get a const reference to the element at position pos, with bounds checking.

reference at(size_type pos)¶: Get a reference to the element at position pos, with bounds checking.

Iterators¶

constexpr const_iterator cbegin() const¶: Get a const iterator to the beginning.

constexpr const_iterator cend() const¶: Get a const iterator to the end.

constexpr const_iterator begin() const¶: Get a const iterator to the beginning, equivalent to cbegin().

constexpr const_iterator end() const¶: Get a const iterator to the end, equivalent to cend().

iterator begin()¶: Get an iterator to the beginning.

iterator end()¶: Get an iterator to the end.

Fast Vector¶

Sequential containers (e.g. std::vector) are very widely used in engineering practice, and therefore its efficiency can have a notable impact to a system’s overall performance. CLUE++ provides an optimized implementation, namely clue::fast_vector, can aims to serve as a drop-in replacement of std::vector in performance-critical paths.

Features¶

Conforming inteface¶

From the standpoint of interface, clue::fast_vector implements all API for std::vector as specified in the C++11 standard. One may refer to the documentation of std::vector for detailed information. Hence, it can be directly used as a replacement of std::vector.

class A {
    // ...
};

using myvec_t = std::vector<A>;
//
// to leverage fast vector, one can simply
// rewrite this definition as
//
//  using myvec_t = clue::fast_vector<A, 4>;
//
// suppose most vectors have a length below 4.
//

// ...

myvec_t a;
a.xxx(); // call certain member functions

Optimized implementation¶

Compared to std::vector, the implementation of clue::fast_vector is optimized in several aspects:

Allows users to specify a customized static capacity SCap, when the number of elements is below SCap, they can be stored in a static array directly embedded in the object (without the need of dynamic allocation). This can substantially speed up the cases that involve a large number of short vectors (but with varying sizes).
For element types that are declared as relocatable, it directly calls memcpy or memmove when performing batch insertion or erasion.
It grows the capacity by a factor of about 1.625 = 1 + 1/2 + 1/8 instead of 2. The choice of this a smaller growth factor is inspired by fbvector.

The `fast_vector` class template¶

class fast_vector¶

Formal:

template<class T,
         size_t SCap=0,
         bool Reloc=is_relocatable<T>::value,
         class Allocator=std::allocator<T> >
class fast_vector final;

Parameters:	T – The element type. SCap – The static capacity. Reloc – Whether the elements are bitwise relocatable. Allocator – The underlying allocator type.

Note

The internal implementation of fast_vector optionally comes with a static array of size SCap. When the number of elements is below SCap, they can be stored in the static array without dynamic memory allocation. By default, SCap == 0, which indicates using dynamic memory whenever the vector is non-empty.
Bitwise relocatability means that an instance of type T can be moved around in the memory without affecting its own integrity. This is the case for most C++ types used in practice. However, for certain types that maintain pointers or references to members, their instances are not relocatable.

CLUE uses a traits struct clue::is_relocatable to determine whether a type is relocatable. For safety, CLUE adopts a conservative approach, that is, to assume all types are NOT relocatable except scalar types. However, users can overwrite this behavior to enable fast movement for a customized type T, either specializing clue::is_relocatable<T> or simply specifying the third template argument Reloc to be true.

Ordered Dict¶

An ordered dict is an associative container (like a hash table) that preserves the input order of the entries, namely, the order of pairs that one visits when traversing from begin() to end() is the same as the order of those pairs being inserted to the dict.

Note

The order-preserving behavior is similar to that of Python’s OrderedDict.

#include <clue/ordered_dict.hpp>

using namespace clue;

ordered_dict<string, int> d;
d["a"] = 1;
d["b"] = 3;
d["c"] = 2;

for (const auto& e: d) {
    std::cout << e.first << " -- " << e.second << std::endl;
}

// This snippet prints:
//
// a -- 1
// b -- 2
// c -- 3

// The dict can also be constructed in other ways,
// e.g. initializer list.

ordered_dict<string, int> d2{{"a", 1}, {"b", 3}, {"c", 2}};

// key/values can be accessed via several methods:

d.at("b");   // -> 3
d.at("x");   // throws std::out_of_range

d.find("b");  // returns a iterator pointing to {"b", 2}
d.find("x");  // returns d.end()

// entries can be added in several different ways:

ordered_dict<string, int> d3;
d3.insert({"a", 1});
d3.emplace("b", 2);      // construct a pair then
                         // decide whether to insert
d3.try_emplace("c", 3);  // when "c" is not found,
                         // it then construct a pair and insert.

// Note: the subtle differences between the behaviors of emplace
// and try_emplace follows that of std::unordered_map.

d3.emplace("a", 5);     // no insertion happens as "a" already existed.
d3.update("a", 5);      // updates the value of d3["a"] to 5
d3["a"] = 5;            // updates the value of d3["a"] to 5

d.insert({{"a", 10}, {"b", 20}}); // insert a series of pairs,
                                  // entries with repeated keys will be
                                  // ignored.

d.update({{"a", 10}, {"b", 20}}); // update from a series of pairs,
                                  // entries with repeated keys will be
                                  // used to overwrite current values.

The `ordered_dict` class template¶

class ordered_dict¶

Formal:

template<class Key,
         class T,
         class Hash = std::hash<Key>,
         class KeyEqual = std::equal_to<Key>,
         class Allocator = std::allocator< std::pair<Key,T> >
        >
class ordered_dict;

Parameters:	Key – The Key type (copy-constructible). T – The mapped type. Hash – The hash functor type. KeyEqual – The functor type for key equality comparison. Allocator – The allocator type.

Note

The implementation of ordered_dict contains a vector of key-value pairs (of class std::pair<Key, T>), and a map from key to index.

The API design of ordered_dict emulates that of std::unordered_map, except that it is a grow-only container, namely, one can insert new entries but cannot remove existing ones.

Member types¶

The class ordered_dict<Key, T, Hash, KeyEqual, Allocator> contains a series of member typedefs as follows:

types	definitions
`key_type`	`Key`
`mapped_type`	`T`
`value_type`	`std::pair<Key, T>`
`size_type`	`std::size_t`
`difference_type`	`std::ptrdiff_t`
`hasher`	`Hash`
`key_equal`	`KeyEqual`
`allocator_type`	`Allocator`
`reference`	`T&`
`const_reference`	`const T&`
`pointer`	`std::allocator_traits<Allocator>::pointer`
`const_pointer`	`std::allocator_traits<Allocator>::const_pointer`
`iterator`	`std::vector<std::pair<Key, T>, Allocator>::iterator`
`const_iterator`	`std::vector<std::pair<Key, T>, Allocator>::const_iterator`

Construction¶

ordered_dict()¶: Default constructor. Constructs an empty dict.

ordered_dict(InputIter first, InputIter last)¶: Constructs a dict from a range of key-value pairs, given by [first, last).

ordered_dict(std::initializer_list<value_type> ilist)¶: Constructs a dict from an initializer_list that contains a series of key-value pairs.

Note

ordered_dict also has a copy constructor, an assignment operator, a destructor and a swap member function, all with default behaviors.

Basic Properties¶

bool empty() const noexcept¶: Get whether the dict is empty (i.e. containing no entries).

size_type size() const noexcept¶: Get the number of key-value entries contained in the dict.

size_type max_size() const noexcept¶: Get the maximum number of entries that can be put into the dict.

bool operator==(const ordered_dict &other) const¶: Test whether two dicts are equal, i.e. their underlying list of key-value pairs are equal.

bool operator!=(const ordered_dict &other) const¶: Test whether two dicts are not equal.

Lookup¶

The elements in a dict can be retrieved by a key or a positional index.

const T &at(const Key &key) const¶

Get a const reference to the corresponding mapped value given a key.

Throw:	An exception of class `std::out_of_range` when the given key is not in the dict.

T &at(const Key &key)¶

Get a reference to the corresponding mapped value given a key.

Throw:	An exception of class `std::out_of_range` when the given key is not in the dict.

const value_type &at_pos(size_type pos) const¶: Get a const reference to the pos-th key-value pair.

value_type &at_pos(size_type pos)¶: Get a reference to the pos-th key-value pair.

T &operator[](const Key &key)¶

Return a reference to the mapped value corresponding to key. When the key is not in the dict, it inserts a new entry (where the key is copied, and the mapped value is constructed by default constructor).

Note:	This is equivalent to `try_emplace(key).first->second`.

T &operator[](Key &&key)¶

Return a reference to the mapped value corresponding to key. When the key is not in the dict, it inserts a new entry (where the key is moved in, and the mapped value is constructed by default constructor).

Note:	This is equivalent to `try_emplace(std::move(key)).first->second`.

const_iterator find(const Key &key) const¶: Locate a key-value pair whose key is equal to key, and return a const iterator pointing to it. If key is not found, it returns end().

iterator find(const Key &key)¶: Locate a key-value pair whose key is equal to key, and return an iterator pointing to it. If key is not found, it returns end().

size_type count(const Key &key) const¶: Count the number of occurrences of those keys that equal key.

Modification¶

void clear()¶: Clear all contained entries.

void reserve(size_type c)¶: Reserve the internal storage to accomodate at least c entries.

std::pair<iterator, bool> emplace(Args&&... args)¶

Construct a new key-value pair from args and insert it to the dict if the key does not exist.

Returns:	a pair comprised of an iterator to the inserted/found entry, and whether the insertion occurs.

std::pair<iterator, bool> try_emplace(const key_type &k, Args&&... args)¶

If the given key k is not found in the dict, insert a new key-value pair whose mapped value is constructed from args, otherwise, no construction and insertion would happen.

Returns:	a pair comprised of an iterator to the inserted/found entry, and whether the insertion occurs.

Note

There exist differences between the behaviors of emplace and try_emplace. Specifically, emplace first constructs a key-value pair from args, and then look-up the key and decide whether to insert the new pair; while try_emplace first look-up the key and then decide whether to construct and insert a new pair. Generally, try_emplace is more efficient when the key already existed.

std::pair<iterator, bool> insert(const value_type &v)¶

Insert a copy of the given pair to the dict if the key v.first is not found.

Returns:	a pair comprised of an iterator to the inserted/found entry, and whether the insertion occurs.

std::pair<iterator, bool> insert(value_type &&v)¶

Insert a move-in pair to the dict if the key v.first is not found.

Returns:	a pair comprised of an iterator to the inserted/found entry, and whether the insertion occurs.

std::pair<iterator, bool> insert(P &&v)¶: Equivalent to emplace(std::forward<P>(v)).

void insert(InputIter first, InputIter last)¶

Insert a range of key-value pairs to the dict.

Note:	Those pairs whose keys already exist will not be inserted.

void insert(std::initializer_list<value_type> ilist)¶

Insert a series of key-value pairs from a given initializer list ilist.

Note:	Those pairs whose keys already exist will not be inserted.

void update(const value_type &v)¶

Update an entry based on the given key-value pair. Insert a new entry if the key v.first is not found.

Note:	`d.update(v)` is equivalent to `d[v.first] = v.second`.

void update(InputIter first, InputIter last)¶: Update entries from a range of key-value pairs.

void update(std::initializer_list<value_type> ilist)¶: Update entries from a series of key-value pairs given by an initializer list ilist.

Iterators¶

constexpr const_iterator cbegin() const¶: Get a const iterator to the beginning.

constexpr const_iterator cend() const¶: Get a const iterator to the end.

constexpr const_iterator begin() const¶: Get a const iterator to the beginning, equivalent to cbegin().

constexpr const_iterator end() const¶: Get a const iterator to the end, equivalent to cend().

iterator begin()¶: Get an iterator to the beginning.

iterator end()¶: Get an iterator to the end.

Note

These iterators are pointing to key-value pairs, of type std::pair<Key, T>.

Keyed Vector¶

A keyed vector is a sequential container that allows constant-time random access (similar to std::vector), where the elements can be accessed by positional indexes or associated keys (e.g. the names).

#include <clue/keyed_vector.hpp>

using namespace clue;

keyed_vector<int, string> v;

v.push_back("a", 10);
v.push_back("b", 20);
v.push_back("c", 30);

// The code above makes a keyed-vector that contains three
// elements: 10, 20, and 30. They are respectively associated
// with keys "a", "b", and "c".

// The elements can be accessed using positional indexes:

v[0];     // -> 10, without bounds-checking
v.at(1);  // -> 20, with bounds-checking
v.at(2);  // -> 30
std::vector<int>(v.begin(), v.end()); // -> {10, 20, 30}

// They can also be accessed using keys:

v.by("a");   // -> 10
v.by("b");   // -> 20
v.by("c");   // -> 30

// Elements can be appended in batch:

keyed_vector<int, string> v2;
v2.extend(v.begin(), v.end());
v2.extend({{"a", 10}, {"b", 20}, {"c", 30}});

// The vector can be directly constructed from ranges/initializers

keyed_vector<int, string> u(v.begin(), v.end());
keyed_vector<int, string> u2{{"a", 10}, {"b", 20}, {"c", 30}};

The `keyed_vector` class template¶

class keyed_vector¶

Formal:

template<class T,
         class Key,
         class Hash=std::hash<Key>,
         class Allocator=std::allocator<T>
        >
class keyed_vector;

Parameters:	T – The element type. Key – The key type. Hash – The hashing functor of keys. Allocator – The allocator type.

Note

The implementation of keyed_vector contains a standard vector of type std::vector<T, Allocator> and a hash map that associates keys with positional indexes.

The API design of this class emulates that of std::vector, except: (1) it allows elements to be accessed by key, using the method by, and (2) it is grow-only, namely, one can add new elements, but cannot remove existing ones.

Difference from `unordered_dict`¶

Whereas both unordered_dict and keyed_vector implement key-value mapping and preserve input order, they are different kinds of containers. Specifically, unordered_dict is a container of std::pair<Key, T> with an API similar to std::unordered_map, while keyed_vector is a container of T with an API similar to std::vector (while additionally allowing indexing by key).

Member types¶

The class keyed_vector<T, Key, Hash, Allocator> contains the following member typedefs:

types	definitions
`key_type`	`Key`
`value_type`	`T`
`size_type`	`std::size_t`
`difference_type`	`std::ptrdiff_t`
`hasher`	`Hash`
`allocator_type`	`Allocator`
`reference`	`T&`
`const_reference`	`const T&`
`pointer`	`std::allocator_traits<Allocator>::pointer`
`const_pointer`	`std::allocator_traits<Allocator>::const_pointer`
`iterator`	`std::vector<T, Allocator>::iterator`
`const_iterator`	`std::vector<T, Allocator>::const_iterator`
`reverse_iterator`	`std::vector<T, Allocator>::reverse_iterator`
`const_reverse_iterator`	`std::vector<T, Allocator>::const_reverse_iterator`

Construction¶

keyed_vector()¶: Construct an empty keyed vector.

keyed_vector(InputIter first, InputIter last)¶: Construct a keyed vector from a range of entries (of type std::pair<Key,T>).

keyed_vector(std::initializer_list<std::pair<Key, T>> ilist)¶: Construct a keyed vector from a list of initial entries (of type std::pair<Key, T>).

Note

keyed_vector also has a copy constructor, an assignment operator, a destructor and a swap member function, all with default behaviors.

Basic Properties¶

bool empty() const noexcept¶: Get whether the vector is empty (i.e. containing no elements).

size_type size() const noexcept¶: Get the number of elements contained in the vector.

size_type max_size() const noexcept¶: Get the maximum number of elements that can be put into the vector.

size_type capacity() const noexcept¶: The maximum number of elements that the current storage can hold without reallocating memory.

bool operator==(const keyed_vector &other) const¶: Test whether two keyed vectors are equal, i.e. the sequence of elements and their keys are equal.

bool operator!=(const keyed_vector &other) const¶: Test whether two keyed vectors are not equal.

Element Access¶

const T *data() const noexcept¶: Get a const pointer to the base of the internal element array.

T *data() noexcept¶: Get a pointer to the base of the internal element array.

const T &front() const¶: Get a const reference to the first element.

T &front()¶: Get a reference to the first element.

const T &back() const¶: Get a const reference to the last element.

T &back()¶: Get a reference to the last element.

const T &at(size_type i) const¶

Get a const reference to the i-th element.

Throw:	an exception of class `std::out_of_range` if `i >= size()`.

T &at(size_type i)¶

Get a reference to the i-th element.

Throw:	an exception of class `std::out_of_range` if `i >= size()`.

const T &operator[](size_type i) const¶: Get a const reference to the i-th element (without bounds checking).

T &operator[](size_type i)¶: Get a reference to the i-th element (without bounds checking).

const T &by(const key_type &k) const¶

Get a const reference to the element corresponding to the key k.

Throw:	an exception of class `std::out_of_range` if the key `k` is not found.

T &by(const key_type &k)¶

Get a reference to the element corresponding to the key k.

Throw:	an exception of class `std::out_of_range` if the key `k` is not found.

const_iterator find(const key_type &k) const¶: Return a const iterator pointing to the element corresponding the key k, or end() if k is not found.

iterator find(const key_type &k)¶: Return an iterator pointing to the element corresponding the key k, or end() if k is not found.

Modification¶

void clear()¶: Clear all contained elements.

void reserve(size_type c)¶: Reserve the internal storage to accomodate at least c elements.

void push_back(const key_type &k, const value_type &v)¶

Push a new element v with key k to the back of the vector.

Both k and v will be copied.

Throw:	an exception of class `std::invalid_argument` if `k` already existed.

void push_back(const key_type &k, value_type &&v)¶

Push a new element v with key k to the back of the vector.

Here, k will be copied, while v will be moved in.

Throw:	an exception of class `std::invalid_argument` if `k` already existed.

void push_back(key_type &&k, const value_type &v)¶

Push a new element v with key k to the back of the vector.

Here, k will be moved in, while v will be copied.

Throw:	an exception of class `std::invalid_argument` if `k` already existed.

void push_back(key_type &&k, value_type &&v)¶

Push a new element v with key k to the back of the vector.

Both k and v will be moved in.

Throw:	an exception of class `std::invalid_argument` if `k` already existed.

void emplace_back(const key_type &k, Args&&... args)¶

Construct a new element at the back of the vector with arguments args.

Here, the associated key k will be copied.

Throw:	an exception of class `std::invalid_argument` if `k` already existed.

void emplace_back(key_type &&k, Args&&... args)¶

Construct a new element at the back of the vector with arguments args.

Here, the associated key k will be moved in.

Throw:	an exception of class `std::invalid_argument` if `k` already existed.

void extend(InputIter first, InputIter last)¶

Append a series of keyed values to the back. An element of the source range should be a pair of class std::pair<Key, T>.

Throw:	an exception of class `std::invalid_argument` when attempting to add a value with a key that already existed.

void extend(std::initializer_list<std::pair<Key, T>> ilist)¶

Append a series of keyed values (from an initializer list) to the back.

Throw:	an exception of class `std::invalid_argument` when attempting to add a value with a key that already existed.

String and text processing¶

String View¶

In the C++ Extensions for Library Fundamentals (N4480), a class template basic_string_view is introduced. Each instance of such a class refers to a constant contiguous sequence of characters (or char-like objects). This class provides a light-weight representation (with only a pointer and a size) of a sub-string that implements many of the methods available for std::string.

The string views are very useful in practice, especially for those applications that heavily rely on sub-string operations (but don’t need to modify the string content). For such applications, string views can be a drop-in replacement of standard strings (i.e. instances of std::string) as they provide a similar set of interface, but are generally much more efficient (they don’t make copies).

This library provides string view classes, where our implementation strictly follows the Technical Specification (N4480), except that all the classes and functions are within the namespace clue (instead of std::experimental). The standard document for this class is available here.

Below is brief description of the types, their members, and other relevant functions.

The `basic_string_view` class template¶

The signature of the class template is as follows:

class basic_string_view¶

Formal:

template<class charT, class Traits>
class basic_string_view;

Parameters:	charT – The character type. Traits – The traits class that specify basic operations on the character type. Here, `Traits` can be omitted, which is, by default, set to `std::char_traits<charT>`.

Four typedefs are defined:

typedef basic_string_view<char> string_view¶

typedef basic_string_view<wchar_t> wstring_view¶

typedef basic_string_view<char16_t> u16string_view¶

typedef basic_string_view<char32_t> u32string_view¶

For ASCII strings with character type char, one should use string_view.

Member types and constants¶

The class basic_string_view<charT, Traits> contains a series of member typedefs as follows:

types	definitions
`traits_type`	`Traits`
`value_type`	`charT`
`pointer`	`const charT*`
`const_pointer`	`const charT*`
`reference`	`const charT&`
`const_reference`	`const charT&`
`iterator`	implementing `RandomAccessIterator`
`const_iterator`	`iterator`
`reverse_iterator`	`std::reverse_iterator<iterator>`
`const_reverse_iterator`	`std::reverse_iterator<const_iterator>`
`size_type`	`std::size_t`
`difference_type`	`std::difference_type`

It also has a member constant npos, defined as size_t(-1), to indicate a certain kind of characters or sub-strings are not found in a finding process. (This is the same as std::string).

Constructors¶

The class basic_string_view<charT, Traits> provides multiple ways to construct a string view. Below is a brief documentation of the member functions. For conciseness, we take string_view for example in the following documentation. The same set of constructors and member functions apply to other instantations of the class template similarly.

constexpr string_view() noexcept¶: Construct an empty string view

constexpr string_view(const string_view &r) noexcept¶

Copy construct a string view from r (default behavior)

Note:	The copy constructor only sets the size and the base pointer, without copying the characters that it refers to.

string_view(const std::string &s) noexcept¶: Construct a view of a standard string s.

constexpr string_view(const charT *s, size_type count) noexcept¶: Construct a view with the base address s and length count.

constexpr string_view(const charT *s) noexcept¶: Construct a view of a null-terminated C-string.

The string_view class also has destructor and assignment operators, with default behaviors.

Basic Properties¶

The string_view class provides member functions to get basic properties:

constexpr bool empty() const noexcept¶: Get whether the string view is empty (i.e. with zero length).

constexpr size_type length() const noexcept¶: Get the length (i.e. the number of characters).

constexpr size_type size() const noexcept¶: Get the length (the same as length()).

constexpr size_type max_size() const noexcept¶: Get the maximum number of characters that a string view can possibly refer to.

Element Access¶

constexpr const_reference operator[](size_type pos) const¶

Get a const reference to the character at location pos.

Note:	The member function `operator []` does not perform bound checking.

const_reference at(size_type pos) const¶

Get a const reference to the character at location pos, with bounds checking.

Throw:	an exception of class `std:out_of_range` if `pos >= size()`.

constexpr const_reference front() const¶: Get a const reference to the first character in the view.

constexpr const_reference back() const¶: Get a const reference to the last character in the view.

constexpr const_pointer data() const noexcept¶

Get a const pointer to the base address (i.e. to the first character).

Note:	For views constructed with default constructor, this returns a null pointer.

Iterators¶

constexpr const_iterator cbegin() const noexcept¶: Get a const iterator to the beginning.

constexpr const_iterator cend() const noexcept¶: Get a const iterator to the end.

constexpr iterator begin() const noexcept¶: Get a const iterator to the beginning, equivalent to cbegin().

constexpr iterator end() const noexcept¶: Get a const iterator to the end, equivalent to cend().

constexpr const_iterator crbegin() const noexcept¶: Get a const reverse iterator to the reversed beginning.

constexpr const_iterator crend() const noexcept¶: Get a const reverse iterator to the reversed end.

constexpr iterator rbegin() const noexcept¶: Get a const reverse iterator to the reversed beginning, equivalent to crbegin().

constexpr iterator rend() const noexcept¶: Get a const reverse iterator to the reversed end, equivalent to crend().

Modifiers¶

void clear() noexcept¶: Clear the view, resetting the data pointer and the size to nullptr and 0 respectively.

void remove_prefix(size_type n) noexcept¶: Exclude the first n characters from the view.

void remove_suffix(size_type n) noexcept¶: Exclude the last n characters from the view.

void swap(string_view &other) noexcept¶: Swap the view with other.

Note

An external swap function are provided for string views, which invokes the member function basic_string_view::swap to perform the swapping.

Conversion, Copy, and Sub-string¶

explicit operator std::string() const¶: Convert the string view to a standard string (by making a copy).

std::string to_string() const¶: Convert the string view to a standard string (by making a copy).

size_type copy(charT *s, size_type n, size_type pos = 0) const¶

Copy the part starting at pos to a buffer s of length n.

Returns:	The number of characters actually copied, which is equal to `min(n, size() - pos)`.

constexpr string_view substr(size_type pos = 0, size_type n = npos) const¶

Get a view of a sub-string (with length bounded by n) that begins at pos.

Returns:	With `pos < size()`, it returns a view of a sub-string, whose length is equal to `min(n, size() - pos)`.
Throw:	an exception of class `std::out_of_range` if `pos >= size()`.

Comparison¶

int compare(string_view sv) const noexcept¶

Compare with another string view sv.

Returns:	`0` when it is equal to `sv`, a negative integer when it is less than `sv` (in lexicographical order), or a positive integer when it is greater than `sv`.

int compare(size_type pos1, size_type n1, string_view sv) const¶: Equivalent to substr(pos1, n1).compare(sv).

int compare(size_type pos1, size_type n1, string_view sv, size_type pos2, size_type n2) const¶: Equivalent to substr(pos1, n1).compare(sv.substr(pos2, n2)).

int compare(const charT *s) const¶: Compare with a null-terminated C-string s.

int compare(size_type pos1, size_type n1, const charT *s) const¶: Equivalent to substr(pos1, n1).compare(s).

int compare(size_type pos1, size_type n1, const charT *s, size_type n2) const¶: Equivalent to substr(pos1, n1).compare(string_view(s, n2)).

Note

These many compare methods may seem redundant. They are there mainly to be consistent with the interface of std::string.

In addition to the compare methods, all comparison operators (including ==, !=, <, >, <=, >=) are provided for comparing string views. These operators return values of type bool.

Find Characters¶

Similar to std::string, string view classes provide a series of member functions to locate characters or sub-strings. These member functions return the index of the found occurrence or string_view::npos when the specified character or sub-string is not found within the view (or part of the view).

size_type find(charT c, size_type pos = 0) const noexcept¶: Find the first occurrence of a character c, starting from pos.

size_type rfind(charT c, size_type pos = npos) const noexcept¶: Find the last occurrence of a character c, in a reverse order, starting from pos, or the end of the string view, if pos >= size().

size_type find_first_of(charT c, size_type pos = 0) const noexcept¶: Find the first occurrence of a character c, starting from pos (same as find(c, pos)).

size_type find_first_of(string_view s, size_type pos = 0) const noexcept¶: Find the first occurrence of a character that is in s, starting from pos.

size_type find_first_of(const charT *s, size_type pos, size_type n) const noexcept¶: Equivalent to find_first_of(string_view(s, n), pos).

size_type find_first_of(const charT *s, size_type pos = 0) const noexcept¶: Equivalent to find_first_of(string_view(s), pos).

size_type find_last_of(charT c, size_type pos = npos) const noexcept¶: Find the last occurrence of a character c, in a reverse order, starting from pos, or the end of the string view, if pos >= size() (same as rfind(c, pos)).

size_type find_last_of(string_view s, size_type pos = npos) const noexcept¶: Find the last occurrence of a character that is in s, in a reverse order, starting from pos (or the end of the string view, if pos >= size()).

size_type find_last_of(const charT *s, size_type pos, size_type n) const noexcept¶: Equivalent to find_last_of(string_view(s, n), pos).

size_type find_last_of(const charT *s, size_type pos = npos) const noexcept¶: Equivalent to find_last_of(string_view(s), pos).

size_type find_first_not_of(charT c, size_type pos = 0) const noexcept¶: Find the first occurrence of a character that is not c, starting from pos.

size_type find_first_not_of(string_view s, size_type pos = 0) const noexcept¶: Find the first occurrence of a character that is not in s, starting from pos.

size_type find_first_not_of(const charT *s, size_type pos, size_type n) const noexcept¶: Equivalent to find_first_not_of(string_view(s, n), pos).

size_type find_first_not_of(const charT *s, size_type pos = 0) const noexcept¶: Equivalent to find_first_not_of(string_view(s), pos).

size_type find_last_not_of(charT c, size_type pos = npos) const noexcept¶: Find the last occurrence of a character that is not c, in a reverse order, starting from pos.

size_type find_last_not_of(string_view s, size_type pos = npos) const noexcept¶: Find the first occurrence of a character that is not in s, in a reverse order, starting from pos.

size_type find_last_not_of(const charT *s, size_type pos, size_type n) const noexcept¶: Equivalent to find_first_not_of(string_view(s, n), pos).

size_type find_last_not_of(const charT *s, size_type pos = npos) const noexcept¶: Equivalent to find_first_not_of(string_view(s), pos).

Find Substrings¶

size_type find(string_view s, size_type pos = 0) const noexcept¶: Find a substring s, starting from pos.

size_type find(const charT *s, size_type pos, size_type n) const noexcept¶: Equivalent to find(substr(s, n), pos).

size_type find(const charT *s, size_type pos = 0) const noexcept¶: Equivalent to find(substr(s), pos).

size_type rfind(string_view s, size_type pos = npos) const noexcept¶

Find a substring s, in a reverse order, starting from pos, or the end of the string view if pos >= size().

Note:	A matched substring is considered as found if its starting position precedes `pos`.

size_type rfind(const charT *s, size_type pos, size_type n) const noexcept¶: Equivalent to rfind(substr(s, n), pos).

size_type rfind(const charT *s, size_type pos = npos) const noexcept¶: Equivalent to rfind(substr(s), pos).

Note

The reason that there are so many find_* methods in slightly different forms is that string views need to be consistent with std::string in the interface, so it can serve as a drop-in replacement.

Extensions of String Functionalities¶

This library provides a set of functions to complement the methods of std::string (or string_view). These functions are useful in many practical applications.

Note

To be consistent with the standard, these extended functionalities are provided as global functions (within the namespace clue) instead of member functions.

Combining string views together with these functionalities would make string analysis much easier. Before going into details, let’s first look at a practical examples.

Suppose, we have a text file like this:

# This is a list of attribues
# The symbol `#` is to indicate comments

bar = 100, 20, 3
foo = 13, 568, 24
xyz = 75, 62, 39, 18

The following code snippet uses the functionalities provided in CLUE++ to parse them into a list of records.

// a simple record class
struct Record {
    std::string name;
    std::vector<int> nums;

    Record(const std::string& name) : name(name) {}

    void add(int v) {
        nums.push_back(v);
    }
};

inline std::ostream& operator << (std::ostream& os, const Record& r) {
    os << r.name << ": ";
    for (int v: r.nums) os << v << ' ';
    return os;
}

// the following code reads the file and parses the content
using namespace clue;

// open a file
std::istringstream fin(filename)

// get first line
char buf[256];
fin.getline(buf, 256);

while (fin) {
    // construct a string view out of buffer,
    // and trim leading and trailing spaces
    auto sv = trim(string_view(buf));

    // process each line
    // ignoring empty lines or comments
    if (!sv.empty() && !starts_with(sv, '#')) {
        // locate '='
        size_t ieq = sv.find('=');

        // note: sub-string of a string view remains a view
        // no copying is done here
        auto name = trim(sv.substr(0, ieq));
        auto rhs = trim(sv.substr(ieq + 1));

        // construct a record
        Record record(name.to_string());

        // parse the each term of right-hand-side
        // by tokenizing
        foreach_token_of(rhs, ", ", [&](const char *p, size_t n){
            int v = 0;
            if (try_parse(string_view(p, n), v)) {
                record.add(v);
            } else {
                throw std::runtime_error("Invalid integer number.");
            }
            return true;
        });

        // print the record
        std::cout << record << std::endl;
    }

    // get next line
    fin.getline(buf, 256);
}

In this code snippet, we utilize five aspects of functionalities in CLUE++:

string_view, which constructs a like-weight view (without making a copy) on a memory block to provide string-related API. For example, you can do sv.find(c) and sv.substr(...). Particularly, sv.substr(...) results in another string view of the sub-part, without making any copies.
trim, which yields another string view, with leading and trailing spaces excluded.
starts_with, which checks whether a string starts with a certain character of sub-string. CLUE++ also provides ends_with to check the suffix, and prefix/suffix to extract the prefixes or suffixes.
foreach_token_of, which performs tokenization in a functional way. In particular, it allows a callback function/functor to process each token, instead of making string copies of all the tokens.
try_parse, which trys to parse a string into a numeric value, and returns whether the parsing succeeded.

For string views, please refer to String View for detailed exposition. Below, we introduce other string-related functionalities provided by CLUE++.

Make string view¶

constexpr view(s)¶

Make a view of a standard string s.

If s is of class std::basic_string<charT, Traits, Allocator>, then the returned object will be of class basic_string_view<charT, Traits>. In particular, if s is of class std::string, the returned type would be string_view.

Prefix and suffix¶

constexpr prefix(s, size_t n)¶

Get a prefix (i.e. a substring that starts at 0), whose length is at most n.

Parameters:	s – The input string `s`, which can be a standard string or a string view. n – The maximum length of the prefix.

This is equivalent to s.substr(0, min(s.size(), n)).

constexpr suffix(s, size_t n)¶

Get a suffix (i.e. a substring that ends at the end of s), whose length is at most n.

Parameters:	s – The input string `s`, which can be a standard string or a string view. n – The maximum length of the suffix.

This is equivalent to s.substr(k, m) with m = min(s.size(), n) and k = s.size() - m.

bool starts_with(str, sub)¶

Test whether a string str starts with a prefix sub.

Here, str and sub can be either a null-terminated C-string, a string view, or a standard string.

bool ends_with(str, sub)¶

Test whether a string str ends with a suffix sub.

Here, str and sub can be either a null-terminated C-string, a string view, or a standard string.

Trim strings¶

trim(str)¶

Trim both the leading and trailing spaces of str, where str can be either a standard string or a string view.

Returns:	the trimmed sub-string. It is a view when `str` is a string view, or a copy of the sub-string when `str` is an instance of a standard string.

trim_left(str)¶

Trim the leading spaces of str, where str can be either a standard string or a string view.

Returns:	the trimmed sub-string. It is a view when `str` is a string view, or a copy of the sub-string when `str` is an instance of a standard string.

trim_right(str)¶

Trim the trailing spaces of str, where str can be either a standard string or a string view.

Returns:	the trimmed sub-string. It is a view when `str` is a string view, or a copy of the sub-string when `str` is an instance of a standard string.

Parse values¶

bool try_parse(str, T &v)¶

Try to parse a given string str into a value v. It returns whether the parsing succeeded.

Parameters:	str – The input string to be parsed, which can be either a C-string, a string view, or a standard string. v – The output variable, which will be updated upon successful parsing.

To be more specific, if the function succeeded in parsing the number (i.e. the given string is a valid number representation for type T), the parsed value will be written to v and it returns true, otherwise, it returns false (the value of v won’t be altered upon failure).

Note:	Internally, this function may call `strtol`, `strtoll`, `strtof`, or `strtod`, depending on the type `T`.

Note

This function allows preceding and trailing spaces in str (for convenience in practice), meaning that "123", "123 ", and " 123\n", etc are all considered valid when parsing an integer. However, empty strings, strings with spaces in the middle (e.g. 123 456), or strings with undesirable characters (e.g. 123a) are considered invalid.

For integers, the function allows base-specific prefixes. For example, "0x1ab" are considered an integer in the hexadecimal form, while "0123" are considered an integer in the octal form.

For floating point numbers, both fixed decimal notation and scientific notation are supported.

For boolean values, the function can recognize the following patterns: "0" and "1", "t" and "f", as well as "true" and "false". Here, the comparison with these patterns are case-insensitive.

Examples:

using namespace clue;

int x;
try_parse("123", x);   // x <- 123, returns true
try_parse("a123", x);  // returns false (x is not updated)

double y;
try_parse("12.75", y);  // y <- 12.75, returns true

bool z;
try_parse("0", z);      // z <- false, returns true
try_parse("false", z);  // z <- false, returns true
try_parse("T", z);      // z <- true, returns true

// in real codes, you may write this in case you don't really know
// exactly what value type to expect

auto s = get_some_string_from_text();
bool x_bool;
int x_int;
double x_real;

if (try_parse(s, x_bool)) {
    std::cout << "got a boolean value: " << x_bool << std::endl;
} else if (try_parse(s, x_int)) {
    std::cout << "got an integer: " << x_int << std::endl;
} else if (try_parse(s, x_real)) {
    std::cout << "got a real number: " << x_real << std::endl;
} else {
    throw std::runtime_error("Can't recognize the value!");
}

Tokenize¶

Extracting tokens from a string is a basic and important task in many text processing applications. ANSI C provides a strtok function for tokenizing, which, however, will destruct the source string. Some tokenizing functions in other libraries may return a vector of strings. This way involves making copies of all extracted tokens, which is often unnecessary.

In this library, we provide tokenizing functions in a new form that takes advantage of the lambda functions introduced in C++11. This new way is both efficient and user friendly. Here is an example:

using namespace clue;

const char *str = "123, 456, 789, 2468";

std::vector<long> values;
foreach_token_of(str, ", ", [&](const char *p, size_t len){
    // directly convert the token to an integer,
    // without making a copy of the token
    values.push_back(std::strtol(p, nullptr, 10));

    // always continue to take in next token
    // if return false, the tokenizing process will stop
    return true;
});

Formally, the function signature is given as below.

void foreach_token_of(str, delimiters, f)¶

Extract tokens from the string str, with given delimiter, and apply f to each token.

Parameters:

str –

The input string, which can be either of the

following type:
- C-string (e.g. const char*)
- Standard string (e.g. std:string)
- String view (e.g. string_view)
delimiters – The delimiters for separating tokens, which can be either a character or a C-string (if a character c matches any char in the given delimiters, then c is considered as a delimiter).
f – The call back function for processing tokens. Here, f should be a function, a lambda function, or a functor that takes in two inputs (the base address of the token and its length), and returns a boolean value that indicates whether to continue.

This function stops when all tokens have been extracted and processed or when the callback function f returns false.

Formatting¶

CLUE provides several convenience functions to facilitate string formatting. These functions are light-weight wrappers based on snprintf and C++’s stringstream. These functions are provided by the header <clue/sformat.hpp>.

sstr(args...)¶

Concatenating multiple arguments into a string, through a string stream (an object of class std::ostringstream).

Note

The arguments here need not be strings. The only requirement is that they can be inserted to a standard output stream.

Examples:

#include <clue/sformat.hpp>

sstr(12);  // -> "12"
sstr(1, 2, 3); // -> "123"
sstr(1, " + ", 2, " = ", 3); // -> "1 + 2 = 3"

struct MyPair {
    int x;
    int y;
};

inline std::ostream& operator << (std::ostream& out, const MyPair& p) {
    out << '(' << p.x << ", " << p.y << ')';
    return out;
}

sstr("a = ", MyPair{1,2}); // -> "a = (1, 2)"

cfmt(fmt, x)¶

Wraps a numeric value x into a light-weight wrapper of class cfmt_t<T>. This wrapper uses snprintf-formatting with pattern fmt, when inserted to a standard output stream.

Examples:

cout << cfmt("%d", 12);   // cout << "12"
cout << cfmt("%.6f", 2);  // cout << "12.000000"

cfmt_s(fmt, args...)¶

Encapsulate the result of snprintf-formatting into a function. This function accepts multiple arguments. It returns an object of class std::string.

Examples:

cfmt_s("%04d", 12);  // -> "0012"
cfmt_s("%d + %d = %d", 1, 2, 3); // -> "1 + 2 = 3"

delimits(seq, delimiter)¶

Wraps a sequence seq into a light-weight wrapper of class Delimits<Seq>. The elements of the sequence will be outputed with a separator delimiter, when the wrapper is inserted to a standard output stream.

Note

Here, seq can be of arbitrary collection type Seq. The only requirement is that Seq provides the begin() and end() methods.

Examples:

std::vector xs{1, 2, 3};
cout << delimits(xs, "+");  // cout << "1+2+3"

std::vector ys{5};
cout << delimits(ys, ",");  // cout << "5"

sstr('[', delimits(xs, ", "), ']');  // -> "[1, 2, 3]"

String Template¶

CLUE provides a light-weight string template engine, by the class stemplate.

This template engine uses {{ name }} to indicate the terms to be interpolated, and accepts a dictionary-like object for interpolation.

clue::stemplate st("{{a}} + {{b}} = {{c}}");

std::unordered_map<std::string, int> dct;
dct["a"] = 123;
dct["b"] = 456;
dct["c"] = 579;

std::cout << st.with(dct);  // directly write to the output stream
st.with(dct).str();         // return a rendered string

Note

Here, st.with(dct) returns a light-weight wrapper that maintains const references to both the template st and the value dictionary dct. When inserted to an output stream, the result is directly written to the output stream. One may also call the str() member function of the wrapper, which would return the rendered string, an object of class std::string.

Text IO¶

The library provides some convenient utilties to read/write text files. These functionalities are implemented in <clue/textio.hpp>.

std::string read_file_content(filename)¶

Read all the content in a file into a string.

Here, filename can be of type const char* or std::string.

class line_stream¶

Line stream class. It wraps a text string into a stream of lines. So one can iterate the lines using STL-style iterators.

The iterated values are of type clue::string_view that provides a view into the part of the text corresponding to the current line. Note: The string view includes the line-delimiter '\n'.

The class has three constructors, respectively accepting a C-string toegther with a length, a C-string, or a standard C++ string.

Example: The following example reads text from a file, and print its lines with line number prefixes.

#include <clue/textio.hpp>
#include <iostream>

using clue::string_view;
using clue::read_file_content;
using clue::line_stream;

int main() {
    std::string text = read_file_content("myfile.txt");

    line_stream lstr(text);
    size_t line_no = 0;
    for (string_view line: lstr) {
        std::cout << ++line_no << ": " << line;
    }
}

Monadic Parser¶

We provide the class mparser to facilitate the implementation of parsers. Specifically, this class implements a light-weight monadic parser combination framework, that allows one to compose basic parsing rules to parse more complex patterns.

Examples¶

Here are two examples on how practical parsers can be implemented with mparser.

The first example is to parse a given string ex in the form of <name> = <value>, where name is a typical identifier and value is an integer. Here, spaces are dealt with using the skip_spaces method.

// the namespace that hosts a number of basic parsing rules
using namespace mpar;

// the variables to store the views of extracted parts
string_view lhs, rhs;

// construct an mparser, and skip leading spaces
mparser mp(ex);
mp = mp.skip_spaces();

// extract left-hand-side
mp = mp.pop() >> identifier() >> pop_to(lhs);

// ensure the existence of '='
// blanks(0) means at least 0 blank characters
mp = mp >> blanks(0) >> ch('=') >> blanks(0);

// extract right-hand-side
mp = mp.pop() >> digits() >> pop_to(rhs);

The second example is to parse a function call, in the form of fun(arg1, arg2, ...), where the arguments can be variable names, or real numbers.

using namespace mpar;

// the variables to store the views of extracted parts
string_view fname, arg;
std::vector<string_view> args;

// construct an mparser and skip leading spaces
auto mp = mparser(ex).skip_spaces();

// extract function name
mp = mp.pop() >> identifier() >> pop_to(fname);
assert(!mp.failed());

// locate the left bracket
mp = mp >> blanks(0) >> ch('(') >> blanks(0);
assert(!mp.failed());

// loop to extract arguments
auto term = either_of(identifier(), realnum());
mp = foreach_term(mp, term, ch(','), [&](string_view e){
    args.push_back(e);
});
assert(!mp.failed() && mp.next_is(')'));

Note

It is noteworthy that parsing is not a pure procedure. When parts are detected/extracted, they need to be processed by other components of a larger program, e.g. being fed to higher-level analysis or translated to other forms. Compared to heavy frameworks, such as ANTLR and Boost Spirit, our light-weight approach is more efficient and easier to embed into a C++ program.

The `basic_mparser` class template¶

The signature of the class template is:

class basic_mparser¶

Formal:

template<typename CharT>
class basic_mparser;

Parameters:	CharT – The character type, e.g. `char` or `wchar_t`.

Two alias types are defined:

typedef basic_mparser<char> mparser¶

typedef basic_mparser<wchar_t> wmparser¶

Within the class, there are several useful public typedefs:

types	definitions
`value_type`	`CharT`
`iterator`	`const CharT*`
`const_iterator`	`const CharT*`
`size_type`	`std::size_t`
`view_type`	`basic_string_view<CharT>`
`string_type`	`basic_string<CharT>`

The mparser maintains three pointers, namely, anchor, begin, and end. The part [anchor, begin) is considered as the matched part, which the parser has scanned, while the part [begin, end) is the remaining part, which the parser may process in future. It also maintains a boolean flag to indicate whether the parsing failed.

Constructors¶

basic_mparser(iterator a, iterator b, iterator e, bool fail = false) noexcept¶

Construct an m-parser with all fields given.

Parameters:	a – The anchor pointer. b – The beginning pointer. e – The pass-by-end pointer. fail – Whether the parser is tagged as failed. Default is `false`.

basic_mparser(view_type sv)¶

Construct an m-parser from a string view.

It sets both anchor and begin to sv.data(), and end to sv.data() + sv.size().

basic_mparser(const string_type &s)¶

Construct an m-parser from a standard string.

It is equivalent to basic_mparser(view_type(s)).

basic_mparser(const CharT *s)¶

Construct an m-parser over a C-string.

It is equivalent to basic_mparser(view_type(s)).

basic_mparser(view_type sv, size_type pos)¶

Construct an m-parser from a string view, starting from pos.

It sets both anchor and begin to sv.data() + pos, and end to sv.data() + sv.size().

basic_mparser(const string_type &s, size_type pos)¶: Equivalent to basic_mparser(view_type(s), pos).

basic_mparser(const CharT *s, size_type pos)¶: Equivalent to basic_mparser(view_type(s), pos).

Note

The string range does not own the memory. It only maintains pointers. Hence, it is important to ensure that the underlying string remains valid throughout its lifetime.

Properties¶

iterator anchor() const¶: Get the anchor pointer (of the matched part).

iterator begin() const¶: Get the beginning pointer (of the remaining part).

iterator end() const¶: Get the pass-by-end pointer.

operator bool() const noexcept¶: Return !failed().

bool failed() const noexcept¶: Return whether the parsing was failed.

size_type matched_size() const noexcept¶: Get the size of the matched part, i.e. [anchor, begin).

bool remain() const noexcept¶: Get whether the remaining part is non-empty, i.e. begin != end.

size_type remain_size() const noexcept¶: Get the size of the remaining part.

CharT operator[](size_type i) const¶: Get the i-th character of the remaining part (without bounds checking).

CharT at(size_type i) const¶: Get the i-th character of the remaining part (with bounds checking).

CharT front() const¶: Get the first character of the remaining part.

view_type matched_view() const noexcept¶: Convert the matched part to a string view.

string_type matched_string() const¶: Convert the matched part to a standard string.

view_type remain_view() const¶: Convert the remaining part to a string view.

bool next_is(CharT c) const noexcept¶

Test whether the next character is c.

Equivalent to !failed() && remain() && front() == c.

bool next_is(view_type sv) const noexcept¶: Test whether the parser is not failed and the remaining part starts with sv.

bool next_is(const char *s) const¶: Equivalent to next_is(view_type(s)).

Manipulation¶

The class basic_mparser provides a series of methods to manipulate the m-parser. Note that these methods do not change the current m-parser, instead, they return the manipulated m-parser as a new one.

basic_mparser pop() const noexcept¶: Pop the matched part, i.e. move anchor to begin.

basic_mparser pop_to(string_view &dst) const noexcept¶: Store the matched part to dst and then pop.

basic_mparser skip_to(iterator p) const¶: Move begin to p.

basic_mparser skip_by(size_type n) const¶

Move begin forward by n characters.

Equivalent to skip_to(begin() + n).

basic_mparser skip(Pred &&pred) const¶: Skip all characters that satisfy pred, i.e. those characters on which pred yields true.

basic_mparser skip_spaces() const noexcept¶

Skip spaces.

Equivalent to skip(chars::is_space).

basic_mparser skip_until(Pred &&pred) const¶: Skip until it reaches the end or hits a character that satisfies pred.

basic_mparser fail() const noexcept¶: Tag the m-parser as failed.

We also provide a set of manipulators, which can be used with the insertion operator, to accomplish similar functionalities. The advantage of such manipulators is that they can be used in a way similar to a matching rule. These manipulators are defined within the namespace clue::mpar.

mpar::pop()¶

Get a manipulator that pops the matched part, moving anchor to begin.

Note:	`m >> mpar::pop()` is equivalent to `m.pop()`.

mpar::pop_to(string_view &dst)¶

Get a manipulator that pops the matched part, and stores it to dst.

Note:	`m >> mpar::pop_to(dst)` is equivalent to `m.pop_to(dst)`.

mpar::skip_by(size_t n)¶

Get a manipulator that skips n characters.

Note:	`m >> mpar::skip_by(n)` is equivalent to `m.skip(n)`.

mpar::skip(const Pred &pred)¶

Get a manipulator that skips all characters that satisfy pred.

Note:	`m >> mpar::skip(pred)` is equivalent to `m.skip(pred)`.

mpar::skip_until(const Pred &pred)¶

Get a manipulator that skips until it reaches the end or hits a character that satisfies pred.

Note:	`m >> mpar::skip_until(pred)` is equivalent to `m.skip_until(pred)`.

Matching Rules¶

basic_mparser operator>>(basic_mparser &m, Rule &&rule) const¶

Monadic binding with a given rule.

Generally, rule is a function that tries to match a pattern with the remaining part (or a leading sub-string thereof). Specifically, rule takes as input the beginning pointer b and pass-by-end pointer e and returns a m-parser (of class basic_mparser<CharT>) that indciates the parsing results.

The returned parser rm should satisfy the following requirement:

rm.anchor() == b
rm.end() == e
rm.begin() indicates the pass-by-end of the matched part.
rm.failed() indicates whether the matching failed.

This binding operator >> works as follows:

If m.failed(), it returns m immediately.
Otherwise, it tries to match the remaining part by calling rm = rule(m.begin(), m.end()). If rm.failed(), it returns m.fail(), otherwise it forwards the beginning pointer of the remaining part to rm.begin(), namely, returning m.skip_to(rm.begin()).

We provide a series of pre-defined rules and combinators. By combining these facilities in different ways, one can derive parsers for different purposes. All such facilities are within the namespace clue::mpar.

ch(const Pred &pred)¶

Get a rule that matches a character satisfying pred.

See Predicates for a set of pre-defined predicates on characters, e.g. chars::is_space, chars::is_digit, etc.

ch(char c)¶

Get a rule that matches a character c.

Note:	This is equivalent to `ch(eq(c))`.

ch_in(const char *s)¶

Get a rule that matches a character containes in s.

Note:	This is equivalent to `ch(in(s))`.

chs(const Pred &pred)¶: Get a rule that matches one or more characters that satisfy pred.

chs(const Pred &pred, int lb)¶

Get a rule that matches a sub-string that with at least lb characters that satisfy pred.

If lb is zero, it can match no character (but still considered as a successful match).

chs(const Pred &pred, int lb, int ub)¶

Get a rule that matches a sub-string that with at least lb and at most ub characters that satisfy pred.

If ub is set to -1, there is no upper limit.

chs_fix(const Pred &pred, int n)¶: Get a rule that matches exactly n characters that satisfy pred.

alphas()¶: Equivalent to chs(chars::is_alpha).

digits()¶: Equivalent to chs(chars::is_digit).

alnums()¶: Equivalent to chs(chars::is_alnum).

blanks()¶: Equivalent to chs(chars::is_blank).

blanks(int lb)¶: Equivalent to chs(chars::is_blank, lb).

term(string_view sv)¶: Get a rule that matches a given string.

term(const CharT *s)¶

Get a rule that matches a given string.

Note:	It is equivalent to `term(basic_string_view<CharT>(s))`.

maybe(const Rule &rule)¶

Get a rule that optionally matches rule.

For a typical rule (except for example chs(pred, 0)), if the leading part of the remaining part is not a match, it will return a failed m-parser. This rule simply returns the current parser (without tagging it as failed) when no match is found.

either_of(const R1 &r1, ...)¶

Construct a rule that combines one or more rules in an either-or way.

Particularly, it tries the given rules one-by-one until it finds a match. If all given rules failed, it returns a the current m-parser tagged as failed.

chain(const R1 &r1, ...)¶: Construct a chain-rule that matches a sequence of patterns.

identifier()¶

Get a rule that matches a typical identifier.

A string is considered as an identifier, if it begins with _ or an alphabetic character, which is then optionally followed by a sequence of characters that are either _, alphabetic, or digits.

integer()¶

Get a rule that matches an integer.

An integer pattern optionally starts with + or -, and then it follows with a sequence of digits.

realnum()¶: Get a rule that matches a real number in decimal or scientific format, e.g. 12, -12.34, 2.5e-6, etc.

List Parsing¶

mparser foreach_term(mparser m, const Term &term, const Sep &sep, F &&f)¶

This function parses a delimited list.

It scans a list according to the given pattern as term1 sep term2 sep ... until it reaches the end or a part that does not satisfy the required pattern. Whenever it encounters a new term, it invokes the input functor f on the term.

Parameters:	m – The input m-parser. term – The rule for matching a term. sep – The rule for matching a separator. f – The functor to be invoked on each term (as a `string_view`).

It returns an m-parser skipped to the end of the matched part.

Optional spaces are allowed between terms and separators.

See the example at the beginning of this document section.

Meta-programming tools¶

Extensions of Type Traits¶

In C++11, a collection of type traits have been introduced into the standard library (in the header <type_traits>). While they are very useful, using these type traits in practice is sometimes cumbersome. For example, to add a const qualifier to a type, one has to write

using const_type = typename std::add_const<my_type>::type;

The need to use typename and ::type introduces unnecessary noise to the code. In C++14, a set of helpers are introduced, such as

template<class T>
using add_const_t = typename add_const<T>::type;

This makes the codes that transform types more concise. In particular, with add_const_t, one can write:

using const_type = add_const_t<my_type>;

In CLUE++, we define all these helpers in the header <clue/type_traits.hpp>, so that they can be used within C++11 environment. In particular, the following helpers are provided. All these backported helpers are within the namespace clue.

Note: Below is just a list. For detailed descriptions of these type traits, please refer to the standard documentation.

// for const-volatility specifiers

template<class T>
using remove_cv_t = typename ::std::remove_cv<T>::type;
template<class T>
using remove_const_t = typename ::std::remove_const<T>::type;
template<class T>
using remove_volatile_t = typename ::std::remove_volatile<T>::type;

template<class T>
using add_cv_t = typename ::std::add_cv<T>::type;
template<class T>
using add_const_t = typename ::std::add_const<T>::type;
template<class T>
using add_volatile_t = typename ::std::add_volatile<T>::type;

// for references

template<class T>
using remove_reference_t = typename ::std::remove_reference<T>::type;
template<class T>
using add_lvalue_reference_t = typename ::std::add_lvalue_reference<T>::type;
template<class T>
using add_rvalue_reference_t = typename ::std::add_rvalue_reference<T>::type;

// for pointers
template<class T>
using remove_pointer_t = typename ::std::remove_pointer<T>::type;
template<class T>
using add_pointer_t = typename ::std::add_pointer<T>::type;

// for sign modifiers

template<class T>
using make_signed_t = typename ::std::make_signed<T>::type;
template<class T>
using make_unsigned_t = typename ::std::make_unsigned<T>::type;

// for arrays

template<class T>
using remove_extent_t = typename ::std::remove_extent<T>::type;
template<class T>
using remove_all_extents_t = typename ::std::remove_all_extents<T>::type;

// static conditions

template<bool B, class T = void>
using enable_if_t = typename ::std::enable_if<B,T>::type;
template<bool B, class T, class F>
using conditional_t = typename ::std::conditional<B,T,F>::type;

// other transformations

template<class T>
using decay_t = typename ::std::decay<T>::type;
template<class... T>
using common_type_t = typename ::std::common_type<T...>::type;
template<class T>
using underlying_type_t = typename ::std::underlying_type<T>::type;
template<class T>
using result_of_t = typename ::std::result_of<T>::type;

Meta-types and Meta-functions¶

Template meta-programming has become an indispensible part of modern C++. In C++11, new features such as Variadic template and Template alias makes meta-programming much more efficient and convenient than before. CLUE++ provides a set of tools to facilitate meta programming, which take full advantage of these new C++ features.

For those who are not familiar with C++ meta-programming, Andrzej has a great blog that provides an excellent introduction of this topic.

Important Note: all meta-programming facilities in CLUE++ are within the namespace clue::meta.

Basic types¶

A set of types to support meta-programming:

// Note: all names below are within the namespace clue::meta

using std::integral_constant;

// Indicator of a C++ type
template<typename T>
struct type_ {
    using type = T;
};

// Extract an encapsulated type
template<typename A>
using get_type = typename A::type;

// Indicator of a nil type (nothing)
struct nil_{};

// Static boolean value
template<bool V>
using bool_ = integral_constant<bool, V>;

using true_  = bool_<true>;
using false_ = bool_<false>;

// Static integral values
template<char  V> using char_  = integral_constant<char,  V>;
template<int   V> using int_   = integral_constant<int,   V>;
template<long  V> using long_  = integral_constant<long,  V>;
template<short V> using short_ = integral_constant<short, V>;

template<unsigned char  V> using uchar_  = integral_constant<unsigned char,  V>;
template<unsigned int   V> using uint_   = integral_constant<unsigned int,   V>;
template<unsigned long  V> using ulong_  = integral_constant<unsigned long,  V>;
template<unsigned short V> using ushort_ = integral_constant<unsigned short, V>;

// Static size value
template<size_t V> using size_ = integral_constant<size_t, V>;

// Extract the value type of a static value.
template<class A>
using value_type_of = typename A::value_type;

Sometimes, it is useful to combine two types. For this purpose, we provide a pair_ type to express a pair of types, as well as meta-functions first and second to retrieve them.

// Note: all names below are within the namespace clue::meta

template<typename T1, typename T2>
struct pair_ {
    using first_type = T1;
    using second_type = T2;
};

template<typename T1, typename T2>
struct first<pair_<T1, T2>> {
    using type = T1;
};

template<typename T1, typename T2>
struct second<pair_<T1, T2>> {
    using type = T2;
};

template<class A> using first_t  = typename first<A>::type;
template<class A> using second_t = typename second<A>::type;

Note

The meta-functions first and second are also specialized for other meta data structures, such as the meta sequence.

Static Index Sequence¶

The library provides useful facilities to construct static index sequence, which is useful for splatting elements of a tuples as arguments.

// index_seq can be used to represent a static sequence of indexes
template<size_t... Inds>
struct index_seq{};

// make_index_seq<N> constructs index_seq<0, ..., N-1>

make_index_seq<0>;  // -> index_seq<>
make_index_seq<1>;  // -> index_seq<1>
make_index_seq<4>;  // -> index_seq<0, 1, 2, 3>

The following example shows how one can leverage make_index_seq to splat tuple arguments.

// suppose you have a function join can accepts arbitrary number of arguments
template<class... Args>
void join(const Args&... args) { /* ... */ }

// the join_tup function can splat elements of a tuple

template<class... Args, size_t... I>
void join_tup_impl(const std::tuple<Args...>& tup, clue::meta::index_seq<I...>) {
    join(std::get<I>(tup)...);
}

template<class... Args>
void join_tup(const std::tuple<Args...>& tup) {
    join_tup_impl(tup, clue::meta::make_index_seq<sizeof...(Args)>{});
}

join_tup(std::make_tuple("abc", "xyz", 123));

Basic functions¶

The library also has a series of meta-functions to work with types or static values.

Arithmetic functions¶

// Note: all names below are within the namespace clue::meta

template<typename A>
using negate = integral_constant<value_type_of<A>, -A::value>;

template<typename A>
using next = integral_constant<value_type_of<A>, A::value+1>;

template<typename A>
using prev = integral_constant<value_type_of<A>, A::value-1>;

template<typename A, typename B>
using plus = integral_constant<value_type_of<A>, A::value + B::value>;

template<typename A, typename B>
using minus = integral_constant<value_type_of<A>, A::value - B::value>;

template<typename A, typename B>
using mul = integral_constant<value_type_of<A>, A::value * B::value>;

template<typename A, typename B>
using div = integral_constant<value_type_of<A>, A::value / B::value>;

template<typename A, typename B>
using mod = integral_constant<value_type_of<A>, A::value % B::value>;

// aliases, to cover the names in <functional>
template<typename A, typename B> using multiplies = mul<A, B>;
template<typename A, typename B> using divides = div<A, B>;
template<typename A, typename B> using modulo = mod<A, B>;

Comparison functions¶

// Note: all names below are within the namespace clue::meta

template<typename A, typename B> using eq = bool_<(A::value == B::value)>;
template<typename A, typename B> using ne = bool_<(A::value != B::value)>;
template<typename A, typename B> using gt = bool_<(A::value >  B::value)>;
template<typename A, typename B> using ge = bool_<(A::value >= B::value)>;
template<typename A, typename B> using lt = bool_<(A::value <  B::value)>;
template<typename A, typename B> using le = bool_<(A::value <= B::value)>;

// aliases, to cover the names in <functional>
template<typename A, typename B> using equal_to      = eq<A, B>;
template<typename A, typename B> using not_equal_to  = ne<A, B>;
template<typename A, typename B> using greater       = gt<A, B>;
template<typename A, typename B> using greater_equal = ge<A, B>;
template<typename A, typename B> using less          = lt<A, B>;
template<typename A, typename B> using less_equal    = le<A, B>;

Logical functions¶

class not_¶: The member constant not_<A>::value is equal to !A::value.

class and_¶: The member constant and_<A, B>::value is true iff both A::value and B::value is true.

class or_¶: The member constant or_<A, B>::value is true iff either A::value or B::value is true.

Note

The meta-functions and_<A, B> and or_<A, B> implement the short-circuit behavior. In particular, when A::value == false, and_<A, B>::value is set to false without examining the internals of B. Likewise, when A::value == true, or_<A, B>::value is set to true without examining the internals of B.

Select¶

C++11 provides std::conditional for static dispatch based on a condition. However, using this type in practice, especially in the cases with multiple branches, is very cumbersome. Below is an example that uses std::conditional to map a numeric value to a signed value type.

#include <type_traits>

template<typename T>
using signed_type =
    typename std::conditional<
        std::is_integral<T>::value,
        typename std::conditional<std::is_unsigned<T>::value,
            typename std::make_signed<T>::type,
            T
        >::type,
        typename std::conditional<std::is_floating_point<T>::value,
            T,
            nil_t
        >::type
    >::type;

With the meta-function select and the helper alias select_t, this can be expressed in a much more elegant and concise way:

#include <clue/meta.hpp>

using namespace clue;

template<typename T>
using signed_type =
    meta::select_t<
        std::is_unsigned<T>,       std::make_signed<T>,
        std::is_signed<T>,         meta::type_<T>,
        std::is_floating_point<T>, meta::type_<T>,
        meta::type_<nil_t> >;

Specifically, meta::select is a variadic class template, described as follows:

select<C1, A1, R> has a member typedef type which is equal to A1::type when C1::value is true, or R::type otherwise.
This meta-function can accept arbitrary odd number of arguments. Generally, select<C1, A1, C2, A2, ..., Cm, Am, R> has a member typedef type which is equal to A1::type when C1::value is true, otherwise, it is equal to A2::type if C2::value is true, and so on. If no conditions are met, it is set to R::type.

A helper alias select_t is provided to further simplify the use:

template<typename... Args>
using select_t = typename select<Args...>::type;

Note

The meta-function select implements a short-circuit behavior. It examines the conditions sequentially, and once it finds a condition that is true, it extracts the next type, and will not continue to examine following conditions.

Variadic Reduction¶

A set of variadic meta-functions are provided to perform reduction over static values.

class meta::sum¶: meta::sum<args...> has a member constant value that equals the sum of argument’s member values.

class meta::prod¶: meta::prod<args...> has a member constant value that equals the product of argument’s member values.

class meta::maximum¶: meta::maximum<args...> has a member constant value that equals the maximum of argument’s member values.

class meta::minimum¶: meta::minimum<args...> has a member constant value that equals the minimum of argument’s member values.

class meta::all¶

meta::all<args...> has a member constant value, which equals true if all argument’s member values are true, or false otherwise.

Note:	`all<>::value == true`.

class meta::any¶

meta::any<args...> has a member constant value, which equals true if any of the argument’s member value is true, or false otherwise.

Note:	`any<>::value == false`.

class meta::count_true¶: meta::count_true<args...> has a member constant value, which equals the number of arguments whose member value is true.

class meta::count_false¶: meta::count_false<args...> has a member constant value, which equals the number of arguments whose member value is false.

class meta::all_same¶: meta::all_same<args...> has a member constant value, which indicates whether all argument types are the same.

Note

The meta-functions all and any both implement the short-circuit behaviors. They won’t look further once the resultant value can be determined.

Meta-sequence: Sequence of Types¶

In meta-programming, it is sometimes useful to process a list of types, in a way that is similar to std::vector. CLUE++ provides facilities to support such operations in compile-time. Like other meta-programming tools, all these facilities are also in the namespace clue::meta.

Meta-sequence¶

In CLUE++, we use a variadic class template meta::seq_, defined below, to indicate a sequence of types.

// Within the namespace clue::meta:
template<typename... Elems> struct seq_;

We provide a series of meta-functions that emulate the std::vector API to work with such a sequence of types. Below is an example that illustrates the use of seq_ and some of the meta-functions working with it.

using namespace clue::meta;
using meta::seq_;
using i1 = meta::int_<1>;
using i2 = meta::int_<2>;
using i3 = meta::int_<3>;
using i4 = meta::int_<4>;

// define a sequence of static values
using s = seq_<i1, i2, i3>;

constexpr size_t n = meta::size<s>::value // n = 3;

using xf = meta::front_t<s>;  // xf is i1
using xb = meta::back_t<s>;   // xb is i3
using x0 = meta::at_t<s, 0>;  // x0 is i1
using x1 = meta::at_t<s, 1>;  // x1 is i2

using r1 = meta::push_back_t<s, i4>;
// r1 is seq_<i1, i2, i3, i4>

using r2 = meta::push_front_t<s, i4>;
// r2 is seq_<i4, i1, i2, i3>

using r3 = meta::pop_front_t<s>;
// r3 is seq_<i2, i3>

using r4 = meta::pop_back_t<s>;
// r4 is seq_<i1, i2>

using rr = meta::reverse<s>;
// rr is seq_<i3, i2, i1>

using rt = meta::transform<meta::next, s>;
// rt is seq_<i2, i3, i4>

constexpr int v1 = meta::sum<s>::value; // v1 = 6;
constexpr int v2 = meta::max<s>::value; // v2 = 3;
constexpr int v3 = meta::min<s>::value; // v3 = 1;

Basic properties¶

class meta::size¶: meta::size< seq_<elems...> > has a member constant value that equals to the number of element types.

class meta::empty¶: meta::empty< seq_<elems...> > has a member constant value that is true when the number of element types is zero, or false otherwise.

Element type access¶

class meta::front¶: meta::front< seq_<elems...> > has a member typedef type corresponding to the first element type.

class meta::back¶: meta::back< seq_<elems...> > has a member typedef type corresponding to the last element type in the sequence.

class meta::at¶: meta::at< seq_<elems...>, I > has a member typedef type corresponding to the I-th element type of the sequence.

class meta::first¶: meta::first< seq_<elems...> > has a member typedef type corresponding to the first element type. (Equivalent to using meta::front).

class meta::second¶: meta::second< seq_<elems...> > has a member typedef type corresponding to the second element type.

Helper aliases are provided for all these meta functions:

// Within the namespace clue::meta:

template<class Seq> using front_t  = typename front<Seq>::type;
template<class Seq> using back_t   = typename back<Seq>::type;
template<class Seq> using first_t  = typename first<Seq>::type;
template<class Seq> using second_t = typename second<Seq>::type;

template<class Seq, size_t N>
using at_t = typename at<Seq, N>::type;

Modifiers¶

class meta::clear¶: meta::clear< seq_<elems...> > has a member typedef type = meta::seq_<>.

class meta::pop_front¶: meta::pop_front< seq_<elems...> > has a member typedef type which is a meta sequence with the first element type excluded.

class meta::pop_back¶: meta::pop_back< seq_<elems...> > has a member typedef type which is a meta sequence with the last element type excluded.

class meta::push_front¶: meta::push_front< seq_<elems...>, X > has a member typedef type which prepends a type X to the front of the input meta sequence.

class meta::push_back¶: meta::push_back< seq_<elems...>, X > has a member typedef type which appends a type X to the back of the input meta sequence.

Helper aliases are provided for all these meta functions:

// Within the namespace clue::meta:

template<class Seq> using clear_t = typename clear<Seq>::type;
template<class Seq> using pop_front_t = typename pop_front<Seq>::type;
template<class Seq> using pop_back_t  = typename pop_back<Seq>::type;

template<class Seq, typename X>
using push_front_t = typename push_front<Seq, X>::type;

template<class Seq, typename X>
using push_back_t = typename push_back<Seq, X>::type;

Sequence reduction¶

All variadic reduction functions are specialized to perform reduction over a sequence, as

template<typename... Elems>
struct sum<seq_<Elems...>> : public sum<Elems...> {};

template<typename... Elems>
struct prod<seq_<Elems...>> : public prod<Elems...> {};

template<typename... Elems>
struct max<seq_<Elems...>> : public max<Elems...> {};

template<typename... Elems>
struct min<seq_<Elems...>> : public min<Elems...> {};

template<typename... Elems>
struct all<seq_<Elems...>> : public all<Elems...> {};

template<typename... Elems>
struct any<seq_<Elems...>> : public any<Elems...> {};

template<typename... Elems>
struct count_true<seq_<Elems...>> : public count_true<Elems...> {};

template<typename... Elems>
struct count_false<seq_<Elems...>> : public count_false<Elems...> {};

Algorithms¶

We also implement a collection of algorithms to work with meta sequences.

class meta::cat¶: meta::cat<S1, S2> has a member typedef type that is a concatenation of two meta sequences S1 and S2.

class meta::zip¶

meta::zip<S1, S2> has a member typedef type that zips two meta sequences S1 and S2 of the same length.

Example:

using namespace clue;
using S1 = meta::seq_<char, int>;
using S2 = meta::seq_<float, double>;

using R = typename zip<S1, S2>::type;
// meta::seq_<
//   meta::pair_<char, float>,
//   meta::pair_<int,  double>
// >

class meta::repeat¶

meta::repeat<X, N> has a member typedef type which is a meta sequence that repeats the type X for N times.

Example:	`meta::repeat<int, 3>::type` is `meta::seq_<int, int, int>`.

class meta::reverse¶

meta::reverse<S> has a member typedef type which is a reversed meta sequence.

Example:	`meta::reverse<meta::seq_<char, short, int>>::type` is `meta::seq_<int, short, char>`.

class meta::transform¶: meta::transform<F, S> has a member typedef type which is the transformed sequence obtained by applying a meta-function F to each element type of S.

class meta::transform2¶: meta::transform2<F, S1, S2> has a member typedef type which is the transformed sequence obtained by applying a meta-function F to each element type of S1 and that of S2.

Examples:

using namespace clue;
using meta::int_;
using meta::seq_;

using S1 = seq_<int_<1>, int_<2>, int_<3>>;
using S2 = seq_<int_<4>, int_<5>, int_<6>>;

using U = typename meta::transform<meta::next, S1>::type;
// U is seq_<int_<2>, int_<3>, int_<4>>

using V = typename meta::transform2<meta::plus, S1, S2>::type;
// V is seq_<int_<5>, int_<7>, int_<9>>

class meta::filter¶: With a member typedef type which is the filtered sequence by retaining the element types X in S for which Pred<X>::value is true.

Examples:

using namespace clue;
using meta::int_;
using meta::seq_;

using S = seq_<int_<1>, int_<2>, int_<3>>;

template<class A>
struct is_odd : public bool_<(A::value % 2 == 1)> {};

using R = typename meta::filter<is_odd, S>::type;
// R is seq_<int_<1>, int_<3>>;

class exists¶: exists<X, S> has a member constant value that indicates whether the type X exists as an element type of S.

class exists_if¶: exists_if<Pred, S> has a member constant value which is true if there exist element types X of S such that Pred<X>::value is true.

class count¶: count<X, S> has a member constant value which is equal to the number of occurrences of a type X in the sequence S.

class count_if¶: count_if<X, S> has a member constant value which is equal to the number of element types X in S that satisfy the condition Pred<X>::value is true.

Helper aliases are provided for all algorithms that transform types:

template<class S1, class S2>   using cat_t    = typename cat<S1, S2>::type;
template<class S1, class S2>   using zip_t    = typename zip<S1, S2>::type;
template<typename X, size_t N> using repeat_t = typename repeat<X, N>::type;

template<class Seq> using reverse_t = typename reverse<Seq>::type;

template<template<typename X> class F, class Seq>
using transform_t = typename transform<F, Seq>::type;

template<template<typename X, typename Y> class F, class S1, class S2>
using transform2_t = typename transform2<F, S1, S2>::type;

template<template<typename X> class Pred, class Seq>
using filter_t = typename filter<Pred, Seq>::type;

Concurrent programming¶

Shared Mutex (Read/write lock)¶

In C++14/C++17, a new kind of mutex, called shared mutex, is introduced.

Unlike other mutex types, a shared mutex has two levels of access:

shared: several threads can share ownership of the same mutex.
exclusive: only one thread can own the mutex.

This is useful in situations where we may allow multiple parallel readers or one writer to operate on a block of data.

As it is part of the future C++ standard, cppreference already has detailed documentation. Below is just a brief summary of the relevant classes and functions. (In CLUE++, we provide a C++11 implementation for these types, and the names are in the namespace clue, instead of std).

Here is an example of how shared_mutex can be used in practice.

using namespace clue;

class MyData {
    std::vector<double> data_;
    mutable shared_mutex mut_;   // the mutex to protect data_;

public:
    void write() {
        unique_lock<shared_mutex> lk(mut_);
        // ... write to data_ ...
    }

    void read() const {
        shared_lock<shared_mutex> lk(mut_);
        // ... read the data ...
    }
};

// --- main program ---

MyData a;

std::thread t_write([&](){
    a.write();
    sleep_for_a_while();
});

std::thread t_read1([&](){
    a.read();
});

std::thread t_read2([&](){
    a.read();
});

// t_read1 and t_read2 can simultaneously read a,
// while t_write is not writing

Class `shared_mutex`¶

class shared_mutex¶

A mutex class that allows multiple thread to maintain shared ownership at the same time, or a thread to maintain exclusive ownership.

Note:	It is a default constructor and a destructor, while the copy constructor and assignment operator are deleted.
Note:	This class is accepted to the C++17 standard.

The table below lists its member functions:

void lock()¶: Locks the mutex (acquires exclusive ownership), blocks if the mutex is not available.

bool try_lock()¶

Tries to lock the mutex.

Returns immediately. On successful lock acquisition returns true, otherwise returns false.

void unlock()¶

Unlocks the mutex.

Note:	The mutex must be locked by the current thread of execution, otherwise, the behavior is undefined.

void lock_shared()¶

Acquires shared ownership of the mutex.

If another thread is holding the mutex in exclusive ownership, a call to lock_shared will block execution until shared ownership can be acquired.

bool try_lock_shared()¶: Tries to lock the mutex in shared mode. Returns immediately. On successful lock acquisition returns true, otherwise returns false.

void unlock_shared()¶

Releases the mutex from shared ownership by the calling thread.

Note:	The mutex must be locked by the current thread of execution in shared mode, otherwise, the behavior is undefined.

Class `shared_timed_mutex`¶

class shared_time_mutex¶

Similar to shared_mutex, shared_timed_mutex allows multiple shared ownership or one exclusive ownership. In addition, it provides the ability to try to acquire the exclusive or shared ownership with a timeout.

Note:	This class is introduced in C++14.

The class shared_timed_mutex provides all the member funtions as in shared_mutex. In addition, it provides the following members:

bool try_lock_for(const std::chrono::duration<Rep, Period> &duration)¶

Tries to lock the mutex (acquire exclusive ownership).

Blocks until specified duration has elapsed or the lock is acquired, whichever comes first. On successful lock acquisition returns true, otherwise returns false.

bool try_lock_until(const std::chrono::time_point<Clock, Duration> &t)¶

Tries to lock the mutex (acquire exclusive ownership).

Blocks until specified due time t has been reached or the lock is acquired, whichever comes first. On successful lock acquisition returns true, otherwise returns false.

bool try_lock_shared_for(const std::chrono::duration<Rep, Period> &duration)¶

Tries to lock the mutex in shared mode (acquire shared ownership).

Blocks until specified duration has elapsed or the lock is acquired, whichever comes first. On successful lock acquisition returns true, otherwise returns false.

bool try_lock_shared_until(const std::chrono::time_point<Clock, Duration> &t)¶

Tries to lock the mutex in shared mode (acquire shared ownership).

Blocks until specified due time t has been reached or the lock is acquired, whichever comes first. On successful lock acquisition returns true, otherwise returns false.

Class `shared_lock`¶

class shared_lock¶

Formal:

template <class Mutex>
class shared_lock;

The class shared_lock is a general-purpose shared mutex ownership wrapper allowing deferred locking, timed locking and transfer of lock ownership.

The shared_lock locks the associated shared mutex in shared mode (to lock it in exclusive mode, std::unique_lock can be used)

Concurrent Counter¶

In concurrent programming, it is not uncommon that some function is triggered by a certain condition (e.g. a number grow beyond certain threshold). CLUE provides a class concurrent_counter to implement this. This class in the header file <clue/concurrent_counter.hpp>.

class concurrent_counter¶

Concurrent counter.

It has a default constructor that initializes the count to zero. There’s another constructor that accepts an initial count.

A concurrent counter is not copyable and not movable.

This class has the following member functions:

long get()¶: Get the current value of the counter;

void set(long v)¶: Set a new count value, and notify all waiting threads.

void inc(long x = 1)¶: Increment the count by x (default is 1), and notify all waiting threads.

void dec(long x = 1)¶: Decrement the count by x (default is 1), and notify all waiting threads.

void reset()¶: Reset the count value to zero, and notify all waiting threads. Equivalent to set(0).

void wait(Pred &&pred)¶: Waits until the count meets the specified condition (pred(count) returns true).

Note

CLUE has provided a series of predicates that can be useful here. (Refer to Predicates for details). For example, if you want to wait until when the count value goes above a certain threshold m, then you may write wait( clue::ge(m) ) (or wait( ge(m) ) when the namespace clue is being used).

void wait(v)¶: Waits until the count hits the given value v. Equivalent to wait( clue::eq(v) ).

bool wait_for(Pred &&pred, const std::chrono::duration &dur)¶

Waits until the count meets the specified condition or the duration dur elapses, whichever comes first.

It returns whether the count meets the condition upon returning.

bool wait_for(long v, const std::chrono::duration &dur)¶: Equivalent to wait_for(clue::eq(v), dur).

bool wait_until(Pred &&pred, const std::chrono::time_point &t)¶

Waits until the count meets the specified condition or the time-out t, whichever comes first.

It returns whether the count meets the condition upon returning.

bool wait_until(long v, const std::chrono::time_point &t)¶: Equivalent to wait_until(clue::eq(v), t).

Examples: The following example shows how a concurrent counter can be used in practice. In this example, a message will be printed when the accumulated value exceeds 100.

clue::concurrent_counter accum_val(0);

std::thread worker([&](){
    for (size_t i = 0; i < 100; ++i) {
        accum_val.inc(static_cast<long>(i + 1));
    }
});

std::thread listener([&](){
    accum_val.wait( clue::gt(100) );
    std::printf("accum_val goes beyond 100!\n");
});

worker.join();
listener.join();

The source file examples/ex_cccounter.cpp provides another example.

Concurrent Queue¶

Concurrent queue is very useful in concurrent programming. For example, task queue can be considered as a special kind of concurrent queue. CLUE implements a concurrent queue class, in header file <clue/concurrent_queue.hpp>.

template<T> class concurrent_queue¶: Concurrent queue class. T is the element type.

This class has a default constructor, but it is not copyable or movable. The class provides the following member functions:

size_t size() const¶: Get the number of elements in the queue (at the point this method is being called).

bool empty() const¶: Get whether the queue is empty (contains no elements).

void synchronize()¶: Block until all updating (e.g. push or pop) are done.

void clear()¶: Clear the queue (pop all remaining elements).

void push(const T &x)¶: Push an element x to the back of the queue.

void push(T &&x)¶: Push an element x (by moving) to the back of the queue.

void emplace(Args&&... args)¶: Construct an element using the given arguments and push it to the back of the queue.

bool try_pop(T &dst)¶: If the queue is not empty, pop the element at the front, store it to dst, and return true. Otherwise, return false immediately.

T wait_pop()¶

Wait until the queue is non-empty, and pop the element at the front and return it.

If the queue is already non-empty, it pops the front element and returns it immediately.

Note

All updating methods, including push, emplace, try_pop, and wait_pop, are thread-safe. It is safe to call these methods in concurrent threads.

Example: The following example shows how to use concurrent_queue to implement a task queue. In this example, multiple concurrent producers generate items to be processed, and a consumer fetches them from a queue and process.

#include <clue/concurrent_queue.hpp>
#include <vector>
#include <thread>
#include <cstdio>

inline void process_item(double v) {
    std::printf("process item %g\n", v);
}

int main() {
    const size_t M = 2;  // # producers
    const size_t k = 10;  // # items per producer
    size_t remain_nitems = M * k;

    clue::concurrent_queue<double> Q;
    std::vector<std::thread> producers;

    // producers: generate items to be processed
    for (size_t t = 0; t < M; ++t) {
        producers.emplace_back([&Q,t,k](){
            for (size_t i = 0; i < k; ++i) {
                double v = i + 1;
                Q.push(v);
            }
        });
    }

    // consumer: process the items
    std::thread consumer([&](){
        while (remain_nitems > 0) {
            process_item(Q.wait_pop());
            -- remain_nitems;
        }
    });

    // wait for all threads to complete
    for (auto& th: producers) th.join();
    consumer.join();
}

Note

To emulate a typical task queue, one may also push functions as elements, and let the consumer invokes each function that it acquires from the queue.

Thread Pool¶

Thread pool is a very important pattern in concurrent programming. It maps multiple tasks to a smaller number of threads. This is generally more efficient than spawning one thread for each task, especially when the number of tasks is large. CLUE provides a thread_pool class in the header file <clue/thread_pool.hpp>.

class thread_pool¶

A thread pool class.

By default, thread_pool() constructs a thread pool with zero threads. thread_pool(n) constructs a thread pool with n threads. One can modify the number of threads using the resize() method later.

A thread pool is not copyable and not movable.

The thread_pool class provides the following member functions:

bool empty() const noexcept¶: Return whether the pool is empty (contains no threads).

size_t size() const noexcept¶: Get the number of threads maintained by the pool.

std::thread &get_thread(size_t i)¶: Get a reference to the i-th thread.

const std::thread &get_thread(size_t i) const¶: Get a const-reference to the i-th thread.

size_t num_scheduled_tasks() const noexcept¶: Get the total number of scheduled tasks (all the tasks that have ever been pushed to the queue).

size_t num_completed_tasks() const noexcept¶: Get the total number of tasks that have been completed.

bool stopped() const noexcept¶: Get whether the thread pool has been stopped (by calling stop()).

bool done() const noexcept¶: Get whether all scheduled tasks have been done.

void resize(n)¶: Resize the pool to n threads.

Note

When n is less than size(), the pool will be shrinked, trailing threads will be terminated and detached.

std::future<R> schedule(F &&f)¶

Schedule a task.

Here, f should be a functor/function that accepts a thread index of type size_t as an argument. This function returns a future of class std::future<R>, where R is the return type of f.

This function would wrap f into a packaged_task and push it to the internal task queue. When a thread is available, it will try to get a task from the front of the internal task queue and execute it.

Note

It is straightforward to push a function that accepts more arguments. One can just wrap it into a closure using C++11’s lambda function.

void synchronize()¶

Block until all current tasks have been completed.

This function does not close the thread pool or stop any threads. After synchronization, one can continue to schedule new tasks.

Note

Multiple threads can synchronize a thread pool at the same time. However, it is not allowed to schedule a task while some one is synchronizing.

void close(bool stop_cmd = false)¶

Close the queue, so that no new tasks can be scheduled.

If stop_cmd is explicitly set to true, it also sends a stopping command to all threads.

Note

This function returns immediately after closing the queue (and optionally sending the stopping command). It won’t wait for the threads to finish (for this purpose, one can call join()).

void close_and_stop()¶: Equivalent to close(true).

void join()¶

Block until all threads finish.

A thread will finish when the current task is completed and then no task can be acquired (the queue is closed and empty) or when it is stopped explicitly by the stopping command.

Note

The thread pool can only be joined when it is closed. Otherwise a runtime error will be raised. Also, when all threads finish, the function, this function will clear the thread pool, resizing it to 0 threads. However, one can call resize(n) to reinstantiate a new set of threads.

void wait_done()¶: Block until all tasks are completed. Equivalent to close(); join();.

void stop_and_wait()¶

Block until all active tasks (those being run) are completed. Tasks that have been scheduled but have not been launched will remain in the queue (but won’t be run by threads).

This is equivalent to close_and_stop(); join();.

One can later call resize() to re-instate a new set of threads to complete the remaining tasks or call clear_tasks() to clear all remaining tasks.

void clear_tasks()¶: Clear all tasks that remain in the queue. This function won’t affect those tasks that are being executed.

Example: The following example shows how to schedule tasks and wait until when they are all done.

#include <clue/thread_pool.hpp>

void my_task(double arg) {
    // some processing ...
}

int main() {
    // construct a thread pool with 4 threads
    clue::thread_pool P(4);

    size_t n = 20;
    for (size_t i = 0; i < n; ++i) {
        double a = // get an argument;

        // tid is the index of the thread
        P.schedule([](size_t tid){ my_task(a); });
    }

    // wait until all tasks are completed
    P.wait_done();
}

Welcome to CLUE++’s documentation!¶

Contents:¶

Basic utilites¶

Optional (Nullable)¶

Types¶

Constructors¶

Modifiers¶

Observers¶

Non-member Functions¶

Comparison¶

Timing¶

Representation of duration¶

Stopwatch¶

Timing functions¶

Value Range¶

The value_range and stepped_value_range class templates¶

Member types¶

Construction¶

Properties and element access¶

Iterators¶

The EnumerableValueTraits concept¶

Predicates¶

Generic predicates¶

Char predicates¶

Float predicates¶

(Demangled) Type Names¶

Miscellaneous Utilities¶

Containers and Views¶

Array View¶

The array_view class template¶

Member types¶

Construction¶

Basic properties and element access¶

Iterators¶

Reindexed View¶

The reindexed_view class template¶

Member types¶

Construction¶

Basic properties and element access¶

Iterators¶

Fast Vector¶

Features¶

Conforming inteface¶

Optimized implementation¶

The fast_vector class template¶

Ordered Dict¶

The ordered_dict class template¶

Member types¶

Construction¶

Basic Properties¶

Lookup¶

Modification¶

Iterators¶

Keyed Vector¶

The keyed_vector class template¶

Difference from unordered_dict¶

Member types¶

Construction¶

Basic Properties¶

Element Access¶

Modification¶

String and text processing¶

String View¶

The basic_string_view class template¶

Member types and constants¶

Constructors¶

Basic Properties¶

Element Access¶

Iterators¶

Modifiers¶

Conversion, Copy, and Sub-string¶

Comparison¶

Find Characters¶

Find Substrings¶

Extensions of String Functionalities¶

Make string view¶

Prefix and suffix¶

Trim strings¶

Parse values¶

Tokenize¶

The `value_range` and `stepped_value_range` class templates¶

The `array_view` class template¶

The `reindexed_view` class template¶

The `fast_vector` class template¶

The `ordered_dict` class template¶

The `keyed_vector` class template¶

Difference from `unordered_dict`¶

The `basic_string_view` class template¶

The `basic_mparser` class template¶

Class `shared_mutex`¶

Class `shared_timed_mutex`¶

Class `shared_lock`¶