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.

[edit] 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).

[edit] 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.

[edit] 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() {}

[edit] Defect reports

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