Re: [boost] ASIO into the standard (was: Re: C++ committee meeting report)

Subject: Re: [boost] ASIO into the standard (was: Re: C++ committee meeting report)
From: Jonathan Wakely (jwakely.boost_at_[hidden])
Date: 2014-07-04 10:44:39

On 4 July 2014 12:44, Niall Douglas wrote:
> There are lots of things going on here. STL allocators were always
> half baked because they were never finished - John Lakos is but one
> of many who took them to all sorts of interesting new places, indeed
> Stepanov's original design had enormous potential. Unfortunately,
> we've ended up stuck with these half finished things, and now they
> are creating slow path performance with std::vector<std::vector<T>>
> because STL containers can't have a noexcept move constructor due to
> allocators!

That's not true, the move constructor always propagates the allocator
so doesn't need to re-allocate. The reason for it not being noexcept
is not because of allocators, and at the last meeting we agreed that
vector and string should have noexcept move constructors, always.

Move assignment might need to reallocate for non-equal allocators, so
that can't always be noexcept (but the implementation can add a
conditional noexcept using the propagate_on_container_move_assignment
trait, if your vendor doesn't do that complain to them :-)