C++ named requirements: LegacyOutputIterator

A LegacyOutputIterator is a LegacyIterator that can write to the pointed-to element.

# Notes

The only valid use of operator* with an output iterator is on the left of an assignment: operator* may return a proxy object, which defines a member operator= (which may be a template).

Equality and inequality may not be defined for output iterators. Even if an operator== is defined, x == y need not imply ++x == ++y.

Assignment through the same value of an output iterator happens only once: algorithms on output iterators must be single-pass algorithms.

Assignment through an output iterator is expected to alternate with incrementing. Double-increment is undefined behavior (C++ standard currently claims that double increment is supported, contrary to the STL documentation; this is LWG issue 2035).

Pure output-only iterator is allowed to declare its iterator_traits::value_type, iterator_traits::difference_type, iterator_traits::pointer, and iterator_traits::reference to be void (and iterators such as std::back_insert_iterator do just thatexcept for difference_type, which is now defined to satisfy std::output_iterator(since C++20)).

# See also

• output_iterator
• Iterator library