Fix std::pair std::is_copy_assignable behavior

[Paolo Carlini]

Hi,

On 4/17/13 8:43 PM, François Dumont wrote:
> On 04/17/2013 09:18 PM, Paolo Carlini wrote:
>> On 4/17/13 8:10 PM, François Dumont wrote:
>>> Hi
>>>
>>>     Here is an other proposal to fix 
>>> std::is_copy_assignable<std::pair<>>.
>> Sorry, I'm still missing something very, very basic: which behavior 
>> is conforming, the current one or what we would get instead? If the 
>> former, is there a DR arguing for the latter?
>>
>> Paolo.
>>
>     The behavior I am targeting is 
> std::is_copy_asignable<std::pair<const int, int>> to be 
> std::false_type for instance. I have added test for many other use 
> cases. More generally I need that when std::is_copy_assignable<T> is 
> std::true_type then writing a = b, with a and b being T, does compile.
>
>     Otherwise this patch just make std::pair match the Standard 
> requirements like at 20.3.2.17. Do you want me to add a bug report in 
> Bugzilla first ?
I'm not talking about GCC's Bugzilla, I meant an ISO DR: if we don't 
have a DR and preferably a vague support of LWG people, I think we 
should not change the behavior of our std::is_copy_assignable only 
because it helps our implementation of other facilities.

Paolo.