9 Iterators library [iterators]

9.3 Iterator requirements [iterator.requirements]

9.3.12 Concept OutputIterator [iterators.output]

The OutputIterator concept is a refinement of Iterator ([iterators.iterator]). It defines requirements for a type that can be used to write values (from the requirement for Writable ([iterators.writable])) and which can be both pre- and post-incremented. However, output iterators are not required to satisfy EqualityComparable.

  template <class I, class T>
  concept bool OutputIterator =
    Iterator<I> &&
    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. OutputIterator<I, T> is satisfied only if *i++ = E; has effects equivalent to:

  *i = E;

Note: Algorithms on output iterators should never attempt to pass through the same iterator twice. They should be single pass algorithms. Algorithms that take output iterators can be used with ostreams as the destination for placing data through the ostream_iterator class as well as with insert iterators and insert pointers.  — end note ]