Subject: Re: [boost] [Tick] Universal quantified concepts/traits
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2014-12-17 18:07:58
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<class F, class T, class U>
>> 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<class Wt, class Wu, class F>
>> struct is_mapped
>> : std::false_type
>> {};
>>
>> template<template<class...> class W, class T, class U, class F>
>> struct is_mapped<W<T>, W<U>, F>
>> : is_callable<F, T, U>
>> {};
>>
>> 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<class F, class Wt>
>> auto requires_(F&& f, Wt&& wt) -> tick::valid<
>> decltype(returns<is_mapped<Wt, _, F>(
>> 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.
HTH,
Vicente