NAME

std::ranges::range - std::ranges::range

Synopsis

Defined in header <ranges>
template< class T >

concept range = requires( T& t ) {
ranges::begin(t); // equality-preserving for forward iterators (since C++20)
ranges::end (t);

};

The range concept defines the requirements of a type that allows iteration over its
elements by providing an iterator and sentinel that denote the elements of the
range.

Semantic requirements

Given an expression E such that decltype((E)) is T, T models range only if

* [ranges::begin(E), ranges::end(E)) denotes a range, and
* both ranges::begin(E) and ranges::end(E) are amortized constant time and do not
alter the value of E in a manner observable to equality-preserving expressions,
and
* if the type of ranges::begin(E) models forward_iterator, ranges::begin(E) is
equality-preserving (in other words, forward iterators support multi-pass
algorithms)

Note: In the definition above, the required expressions ranges::begin(t) and
ranges::end(t) do not require implicit expression variations.

Example

// Run this code

#include <ranges>
#include <vector>
#include <iostream>

template <typename T>
struct range_t : private T {
using T::begin, T::end; /*...*/
};
static_assert(std::ranges::range< range_t<std::vector<int>> >);

template <typename T> struct scalar_t { T t{}; /* no begin/end */ };
static_assert(not std::ranges::range< scalar_t<int> >);

int main() {
if constexpr (range_t<std::vector<int>> r; std::ranges::range<decltype(r)>) {
std::cout << "r is a range\n";
}

if constexpr (scalar_t<int> s; not std::ranges::range<decltype(s)>) {
std::cout << "s is not a range\n";
}
}

Output:

r is a range
s is not a range