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

| | | | | -------------------------------------------------------------------------------------------------------------------------------------------- | | ------------- | | template< class T > concept approximately_sized_range = ranges::range<T> && requires(T& t) { ranges::reserve_hint(t); }; | | (since C++26) |

The approximately_sized_range concept specifies the requirements of a range type that can estimate its size in constant time with the reserve_hint function.

[edit] Semantic requirements

Given an lvalue t of type std::remove_reference_t<T>, T models approximately_sized_range only if

• ranges::reserve_hint(t)

• has amortized constant-time complexity,

• does not alter the value of t in a manner observable to equality-preserving expressions, and

• has a value that is not negative and is representable in ranges::range_difference_t<T>, and

• if ranges::iterator_t<T> models forward_iterator, ranges::reserve_hint(t) is well-defined regardless of the evaluation of ranges::begin(t) (in other words, a single-pass approximately sized range may support a call to reserve_hint only before the first call to begin, but a forward range must support size at all times).

[edit] Notes

[edit] Example

[edit] See also