Re: [boost] [type_traits] common_type and SFINAE

Subject: Re: [boost] [type_traits] common_type and SFINAE
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-10-04 12:15:17

Le 04/10/12 15:02, Jeffrey Lee Hellrung, Jr. a écrit :
> On Thu, Oct 4, 2012 at 12:28 AM, Lorenzo Caminiti <lorcaminiti_at_[hidden]>wrote:
>
>> Hello all,
>>
>> common_type<T, U>::type is defined in a way that gives a hard compiler
>> error if T and U do not have a common type (this is also how
>> common_type is implemented in C++11).
>>
>> An alternative design (I'm not sure if implementable) would have been
>> to not define the type member in case T and U have no common type.
>> This way I could use SFINAE to detect if common_type<T, U>::type does
>> not exist and therefore if T and U have not common type -- so to
>> implement N3351's concept Common<T, U>.
>>
>> Is there a way to implement this alternative design?
>>
> Do you also need this in C++03?
>
Even if Lorenzo doesn't needs it, it will be great to have it in Boost. 
Jeffrey, do you have something that is working already?

Best,
Vicente