Rb_tree constructor optimization

[François Dumont]

I realized there was no test on the noexcept qualification of the move 
constructor with allocator.

I added some and found out that patch was missing a noexcept 
qualification at _Rb_tree level.

Here is the updated patch fully tested, ok to commit ?

François


On 13/09/2017 21:57, François Dumont wrote:
> On 08/09/2017 17:50, Jonathan Wakely wrote:
>>
>> Since we know __a == __x.get_allocator() we could just do:
>>
>>      _Rb_tree(_Rb_tree&& __x, _Node_allocator&&, true_type)
>> noexcept(is_nothrow_move_constructible<_Rb_tree_impl<_Compare>>::value)
>>      : _M_impl(std::move(__x._M_impl))
>>      { }
>>
>> This means we don't need the new constructor.
>
>     You want to consider that a always equal allocator is stateless 
> and so that the provided allocator rvalue reference do not need to be 
> moved. IMHO you can have allocator with state that do not participate 
> in comparison like some monitoring info.
>
>     I'm not confortable with that and prefer to keep current behavior 
> so I propose this new patch considering all your other remarks.
>
>     I change noexcept qualification on [multi]map/set constructors to 
> just rely on _Rep_type constructor noexcept qualification to not 
> duplicate it.
>
> François
>
>



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