[PATCH] D38757: [libc++] Fix PR34898 - vector iterator constructors and assign method perform push_back instead of emplace_back.

David L. Jones via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Fri Oct 13 17:06:28 PDT 2017

dlj requested changes to this revision.
dlj added a comment.
This revision now requires changes to proceed.

Hmm, looking more at this change... while it does make the behaviour consistent for Forward and Input iterators, I think it's just making them both do the wrong thing.

Specifically, based on this:

"... i and j denote iterators satisfying input iterator requirements and refer to elements implicitly convertible to value_­type..."


So, for example, in test_emplacable_concept, the vector constructor should be diagnosed, because there is no way to *implicitly* convert from the dereferenced iterator type to the inserted type. The selected constructor is explicit. Using emplacement just omits a *second* potentially-expensive conversion: the explicit constructor behaviour (invoked through forwarding) may still be undesired.


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