std::ranges::range - cppreference.com (original) (raw)

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

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   // A minimum range struct SimpleRange { int* begin(); int* end(); }; static_assert(std::ranges::range);   // Not a range: no begin/end struct NotRange { int t {}; }; static_assert(!std::ranges::range);   // Not a range: begin does not return an input_or_output_iterator struct NotRange2 { void* begin(); int* end(); }; static_assert(!std::ranges::range);   int main() {}

[edit] Defect reports

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