std::ranges:: range

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.