This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 118e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025年11月05日
[Moved to DR at October 2002 meeting.]
Paragraph 9 of 13.10.3.6 [temp.deduct.type] enumerates the forms that the types P and A need to have in order for template argument deduction to succeed.
For P denoting a pointer to function the paragraph lists the following forms as allowing for template argument deduction:
type(*)(T) T(*)() T(*)(T)
On the other hand, no provision has been made to accommodate similar cases for references to functions, which in light of the wording of 13.10.3.6 [temp.deduct.type] paragraph 11 means that the program below is ill-formed (some of the C++ compilers do not reject it however):
template<typename Arg, typename Result, typename T>
Result foo_r(Result(& rf)(Arg), T x)
{ return rf(Arg(x)); }
template<typename Arg, typename Result, typename T>
Result foo_p(Result(* pf)(Arg), T x)
{ return pf(Arg(x)); }
#include <iostream>
int show_arg(char c)
{
std::cout << c << ' ';
if(std::cout) return 0;
return -1;
}
int main()
{
// The deduction
int (& rf1)(int(&)(char), double) = foo_r; // shall fail here
// While here
int (& rf2)(int(*)(char), double) = foo_p; // it shall succeed
return rf2(show_arg, 2);
}
Proposed resolution (10/01, same as suggested resolution):
In the list of allowable forms for the types P and A in paragraph 9 of 13.10.3.6 [temp.deduct.type] replace
type(*)(T) T(*)() T(*)(T)
by
type(T) T() T(T)