insert_iterator and ostreambuf_iterator don't properly support *o++ = t;

[CaseyCarter]

See the discussion at CaseyCarter/cmcstl2#60 (comment). Both iterators internally store state that must be updated on each write. We made a blanket change to have output iterators' operator++(int) return a copy instead of a reference after the discussion in #137 (and IIRC discussion with LWG at Kona) we broke insert_iterator and ostreambuf_iterator. The expression *o++ = t results in updating the state of the temporary immediately before throwing it on the floor. Later use of the iterator sees the "old" state and does terrible things.

The fix is to change the postfix increment of at least insert_iterator and ostreambuf_iterator, if not all of the output iterators specified in the TS, to again return by reference as in Standard C++.

Proposed Resolution

Adopt P0541.

[ericniebler]

Will be addressed by P0541. See https://github.com/ericniebler/stl2/blob/master/ext/post_inc/post_inc.md for wording.

[ericniebler]

P0541 was moved to ready in Kona.