23 Iterators library [iterators]

23.3 Iterator requirements [iterator.requirements]

23.3.4 Iterator concepts [iterator.concepts] Concept output_­iterator [iterator.concept.output]

The output_­iterator concept defines requirements for a type that can be used to write values (from the requirement for indirectly_­writable ([iterator.concept.writable])) and which can be both pre- and post-incremented.
[Note 1:
Output iterators are not required to model equality_­comparable.
— end note]
template<class I, class T> concept output_­iterator = input_­or_­output_­iterator<I> && indirectly_­writable<I, T> && requires(I i, T&& t) { *i++ = std::forward<T>(t); // not required to be equality-preserving };
Let E be an expression such that decltype((E)) is T, and let i be a dereferenceable object of type I.
I and T model output_­iterator<I, T> only if *i++ = E; has effects equivalent to: *i = E; ++i;
[Note 2:
Algorithms on output iterators should never attempt to pass through the same iterator twice.
They should be single-pass algorithms.
— end note]