On Mon, Oct 8, 2012 at 6:44 AM, Louis Dionne <louis.dionne92@gmail.com> wrote:
Lorenzo Caminiti <lorcaminiti <at> gmail.com> writes:
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?
While this is not directly linked to your question, I have implemented some concepts using SFINAE so you can write stuff like: template <typename T> typename std::enable_if<LessThanComparable<T>::value>::type func() { }
What I did works only in C++11. You may take a look at what I did here: www.github.com/ldionne/duck
I'll be glad if this can be of any help. Please do not hesitate to contact me for anything.
Thanks. FYI, this is definitely relevant to the email thread "[boost] [contract] toward N3351 concepts" and probably to the one about Boost.Generic as well. --Lorenzo