std::ranges::range

template< class T >
concept range = requires( T& t ) {
    ranges::begin(t); // equality-preserving for forward iterators
    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).

Notes

A typical range class only needs to provide two functions:

1. A member function begin() whose return type models input_or_output_iterator.
2. A member function end() whose return type models sentinel_for<It>, where It is the return type of begin().

Alternatively, they can be non-member functions, to be found by argument-dependent lookup.

Example

#include <ranges>

// A minimum range
struct SimpleRange
{
    int* begin();
    int* end();
};
static_assert(std::ranges::range<SimpleRange>);

// Not a range: no begin/end
struct NotRange
{
    int t {};
};
static_assert(!std::ranges::range<NotRange>);

// Not a range: begin does not return an input_or_output_iterator
struct NotRange2
{
    void* begin();
    int* end();
};
static_assert(!std::ranges::range<NotRange2>);

int main() {}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.