Proposed resolution:

This wording is relative to N4023.

1. Change Table 3, [meta.trans.other] in the Library TS as indicated:

   Table 3 — Other type transformations

   Template	Condition	Comments
   …
   template <class Fn, class... ArgTypes> struct invocation_type<Fn(ArgTypes...)>;	Fn and all types in the parameter pack ArgTypes shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound.	The nested typedef invocation_type<Fn(ArgTypes...)>::type shall be defined as follows. If raw_invocation_type<Fn(ArgTypes...)>::type does not exist, there shall be no member typedef type. Otherwise: Let A1, A2, … denote ArgTypes... Let R(T1, T2, …) denote raw_invocation_type_t<Fn(ArgTypes...)> Then the member typedef type shall name the function type R(U1, U2, …) where Ui is decay_t<Ai> if declval<Ai>() is an rvalue otherwise Ti. If raw_invocation_type<Fn(ArgTypes...)>::type is the function type R(T1, T2, …) and Fn is a pointer to member type and T1 is an rvalue reference, then R(decay<T1>::type, T2, …). Otherwise, raw_invocation_type<Fn(ArgTypes...)>::type.

[ 2013-06-21 Rapperswil ]

Accept for Fundamentals TS Working Paper

[ 2014-06-18, Rapperswil ]

Mike Spertus, Richard Smith, Jonathan Wakely, and Jeffrey Yasskin suggest improved wording.

This wording is relative to N3908.

1. Change Table 3, [meta.trans.other] in the Library TS as indicated:

   Table 3 — Other type transformations

   Template	Condition	Comments
   …
   template <class Fn, class... ArgTypes> struct invocation_type<Fn(ArgTypes...)>;	Fn and all types in the parameter pack ArgTypes shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound.	If A1, A2,... denotes ArgTypes... and raw_invocation_type<Fn(ArgTypes...)>::type is the function type R(T1, T2, ...) then let Ui be decay<Ai>::type if Ai is an rvalue otherwise Ti. If and Fn is a pointer to member type and T1 is an rvalue reference, then let U1 be R(decay<T1>::type, T2, ...). Otherwise, raw_invocation_type<Fn(ArgTypes...)>::type The member typedef type shall equal R(U1, U2, ...).

Addresses: fund.ts

invocation_type falls short of its stated goals in the following case. Using the notation of Invocation type traits, consider

void f(int const& i);
more_perfect_forwarding_async(f, int(7)); // Oops. Dangling reference because rvalue gone when async runs

This was always the advertised intent of the proposal, but while the language reflects this for the first parameter in the case of a member pointer, it failed to include corresponding language for other parameters.