std::vector allocator-extended move constructor

[Jonathan Wakely]

On 15 November 2013 12:17, Jonathan Wakely wrote:
> On 15 November 2013 12:11, Jonathan Wakely wrote:
>> The good news is that if all instances of the allocator type compare
>> equal then the _Base will just move some pointers, so we can have a
>> conditional noexcept:
>>       noexcept(_Alloc_traits::_S_always_equal())
>>
>> The bad news is that it's not currently exception-safe.  I should have
>> used __uninitialized_copy_a there.  If moving any element throws an
>> exception then we leak any already-moved elements.
>
> Correction, we don't leak, as __uninitialized_copy_a will destroy
> them, but we do modify the __rv object, so we don't have the strong
> guarantee.  I'm not sure if that constructor is supposed to provide
> the strong guarantee or not.

Since it's an rvalue I don't think we need to preserve its contents
even if an exception is thrown, so I'm going to add the noexcept and
not change the call to __uninitialized_move_a.

One day I hope I'll be able to stop thinking about allocators ...