vector::assign(Iter first, Iter last) should be implemented more efficiently

[kariya_mitsuru@…]

Current implementation of vector::assign(Iter first, Iter last) is same behavior whether Iter is ForwardIterator or not. (First, overwrite to current elements, then erase or insert)

But if Iter is ForwardIterator and capacity() < distance(first, last), it is only necessary to discard old buffer (including its contents) and allocate new buffer which capacity is at least distance(first, last).

Note: according to C++11 specification, value_type need not be MoveInsertable into Container if Iter is ForwardIterator.

[Ion Gaztañaga]

Reviewing old bugs. Seems like this was fixed in commit:

​https://github.com/boostorg/container/commit/f2947c115eca4a8d5da0340e469a87d09588718c

and official at least since Boost 1.56. Thanks for the report.