[ 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 and provides concrete wording ]

I'm strongly in favour for this change to possibly allow for a future "pure" is_callable trait that solely describes function call-like expressions.

Previous resolution [SUPERSEDED]:

This wording is relative to N4640.

1. Modify [meta.type.synop], header <type_traits> synopsis, as indicated:

   […]
   // 20.15.6, type relations
   […]
   
   template <class, class R = void> struct is_invocablecallable; // not defined
   template <class Fn, class... ArgTypes, class R>
   struct is_invocablecallable<Fn(ArgTypes...), R>;
   
   template <class, class R = void> struct is_nothrow_invocablecallable; // not defined
   template <class Fn, class... ArgTypes, class R>
   struct is_nothrow_invocablecallable<Fn(ArgTypes...), R>;
   
   […]
   
   // 20.15.6, type relations
   […]
   template <class T, class R = void> constexpr bool is_invocablecallable_v
   = is_invocablecallable<T, R>::value;
   template <class T, class R = void> constexpr bool is_nothrow_invocablecallable_v
   = is_nothrow_invocablecallable<T, R>::value;
   […]
   

2. Modify [meta.rel], Table 44 — "Type relationship predicates", as indicated:

   Table 44 — Type relationship predicates

   […]
   template <class Fn, class... ArgTypes, class R> struct is_invocablecallable< Fn(ArgTypes...), R>;	[…]	[…]
   template <class Fn, class... ArgTypes, class R> struct is_nothrow_invocablecallable< Fn(ArgTypes...), R>;	is_invocablecallable_v< Fn(ArgTypes...), R> is true […]	[…]

is_callable is not a good name because it implies F(A...) instead of INVOKE(F, A...)

Proposed change: Rename is_callable to is_invocable and rename is_nothrow_callable to is_nothrow_invocable.