Re: [boost] [Tick] Universal quantified concepts/traits

17 Dec 2014

      Le 17/12/14 07:20, Vicente J. Botet Escriba a écrit :
...
Le 16/12/14 22:53, paul Fultz a écrit :
...
Ok, I think I understand what you are aksing for. This how I would 
approach
the problem using Tick. It does require defining different traits to get
there(I am not sure how it could be done all in one take). First, I 
would
define `is_callable` that checks if a function is called with `T` and 
returns
`U`:
TICK_TRAIT(is_callable)
     {
         template
         auto requires_(F&& f, T&& t, U&&) -> tick::valid<
decltype(returns<U>(f(std::forward<T>(t))))
         >;
     };
Next I would write a trait that checks if the two types, `Wt` and 
`Wu`, are
mapped like `W<T> -> W<U>` and that the function takes `T` and 
returns `U`:
template
     struct is_mapped
     : std::false_type
     {};
template class W, class T, class U, class F>
     struct is_mapped
     : is_callable
     {};
And then I would write the `is_functor` to call the `map` function 
and check
that it returns a mapped type:
TICK_TRAIT(is_functor)
     {
         template
         auto requires_(F&& f, Wt&& wt) -> tick::valid<
             decltype(returns(
                 map(f, std::forward<Wt>(wt))
             ))
         >;
     };
Does that make sense? Is this what you are asking for?
No, this trait has two parameters F and Wt. I'm looking for a trait 
with a single parameter W, the type constructor. Maybe I'm looking for 
a thing that should not exists ;-)
This SO question presents the same context.

http://stackoverflow.com/questions/23659382/specifying-a-concept-for-a-type-...

HTH,
Vicente