This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2024-11-11
It is not clear whether the following is well-formed or not:
void foo(){} template<class T> void deduce(const T*) { } int main() { deduce(foo); }
Implementations vary in their treatment of this example.
Proposed resolution (April, 2013):
Change 13.10.3.6 [temp.deduct.type] paragraph 18 as follows:
A template-argument can be deduced from a function, pointer to function, or pointer to member function type. [Note: cv-qualification of a deduced function type is ignored; see 9.3.4.6 [dcl.fct]. —end note] [Example:
template<class T> void f(void(*)(T,int)); template<class T> void f2(const T*); template<class T> void foo(T,int); void g(int,int); void g(char,int); void g2(); void h(int,int,int); void h(char,int); int m() { f(&g); // error: ambiguous f(&h); // OK: void h(char,int) is a unique match f(&foo); // error: type deduction fails because foo is a template f2(g2); // OK: cv-qualification of deduced function type ignored }—end example]
Additional note, November, 2014:
Concern was expressed regarding the proposed resolution over its treatment of an example like the following:
template<typename T> struct tuple_size {}; template<typename T> struct tuple_size<T const>: tuple_size<T> {}; tuple_size<void()> t;
In this case T const is always considered to be more specialized for void(), leading to infinite self-derivation.
The issue has been returned to "open" status for further consideration.
Notes from the May, 2015 meeting:
The consensus of CWG was that the cv-qualification of the argument and parameter must match, so the original example should be rejected.