Re: [boost] [type_traits] type_traits for types with operator().

Subject: Re: [boost] [type_traits] type_traits for types with operator().
From: Jason Roehm (jasonr_at_[hidden])
Date: 2014-01-29 13:42:51

On 01/29/2014 12:28 PM, John Maddock wrote:
>> Recently I looked for type_traits for callable classes. It so strange, I
>> didn't find such traits. Most likely, I just missed them or something 
>> like
>> them.
>>
>> I actually don't know is there a real need for them. Anyway I tried to
>> write such traits at least for practice and metaprogramming training. I
>> tested them with gcc, clang and msvc2010. I would appreciate if you 
>> looked
>> at the code. Here is the
>> link<https://github.com/AntonBikineev/is_functional/> to
>> my github repository.
>>
>> It's cool that they can see hidden generated operator() of lambdas 
>> closure
>> type.
>
> My apologies for not replying before Anton.
>
> This looks cool.  However what does it detect?  Any operator() or 
> nullary operator()?
>
> A better C++11 style interface *if* it can be implemented would be 
> something like:
>
> template <class F, class Args...>
> struct is_callable;
>
> Which inherits from true_type only if F is callable with arguments 
> Args...

There has been some discussion on implementing this sort of interface on 
this mailing list, some in the last few weeks and some closer to a year 
ago, IIRC. I believe there is at least one implementation out there that 
provides a has_call trait. As you pointed out, though, there are a lot 
of cases to handle, and I'm not sure that it covers all of the bases.

Jason