[ 2017-03-12, post-Kona ]

Resolved by p0604r0.

[ 2017-02-24, Daniel comments ]

I suggest to apply the paper d0604r0 instead, available on the Kona LWG wiki.

[ 2017-02-22, Daniel comments ]

LWG 2895 provides now wording for this issue and for LWG 2928 as well.

The trick of encoding a functor and argument types as a function signature for is_callable and result_of loses cv information on argument types, fails for non-decayed function types, and is confusing. E.g.,

typedef int MyClass::*mp; result_of_t<mp(const MyClass)>;
// should be const, but isn't
typedef int F(double); is_callable<F(float)>; // ill-formed

Minimal change:

Replace is_callable<Fn(ArgTypes...)> with is_callable<Fn, ArgTypes...> and replace is_callable<Fn(ArgTypes...), R> with is_callable_r<R, Fn, ArgTypes...>. Do the same for is_nothrow_callable.

Preferred change:

All of the above, plus deprecate result_of<Fn(ArgTypes...)> and replace it with result_of_invoke<Fn, ArgTypes...>

See also LWG 2895.