[Bug c++/53506] New: Variadic templates in combination with function pointer problem

[Bug c++/53506] New: Variadic templates in combination with function pointer problem

[o.mangold at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53506

             Bug #: 53506
           Summary: Variadic templates in combination with function
                    pointer problem
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: o.mangold@googlemail.com


The example code below appears to be correct to me, but does not compiler with
g++. I tried it also with Intel compiler 12.1, and icc compiles it just fine.

Neither the first, nor the second version of the call of a() seems to work. It
can't deduce the template args from the function pointer and also does not
accept explicit specification. I had expected at least the second version of
the call to work. Is gcc wrong here or icc?

> icpc -strict-ansi -std=c++0x fpointers.cxx

> g++ -std=c++11 fpointers.cxx 
fpointers.cxx: In function ‘int main()’:
fpointers.cxx:17:18: error: no matching function for call to ‘A<int>::a(int
(&)(int, int), int)’
fpointers.cxx:17:18: note: candidate is:
fpointers.cxx:5:3: note: template<class RES, class ... FARGS> static void
A::a(RES (*)(FARGS ..., SARGS ...), FARGS ...) [with RES = RES; FARGS = {FARGS
...}; SARGS = {int}]
fpointers.cxx:5:3: note:   template argument deduction/substitution failed:
fpointers.cxx:17:18: note:   candidate expects 1 argument, 2 provided
fpointers.cxx:18:27: error: no matching function for call to ‘A<int>::a(int
(&)(int, int), int)’
fpointers.cxx:18:27: note: candidate is:
fpointers.cxx:5:3: note: template<class RES, class ... FARGS> static void
A::a(RES (*)(FARGS ..., SARGS ...), FARGS ...) [with RES = RES; FARGS = {FARGS
...}; SARGS = {int}]
fpointers.cxx:5:3: note:   template argument deduction/substitution failed:
fpointers.cxx:18:27: note:   candidate expects 1 argument, 2 provided

--- fpointers.cxx ---
template<typename... SARGS>
struct A
{
  template<typename RES,typename... FARGS> static void
  a(RES(*func)(FARGS...,SARGS...),FARGS...)
  {
  }
};

int foo(int,int)
{
  return 0;
}

int main()
{
  A<int>::a(foo,0);
  A<int>::a<int,int>(foo,0);
  return 0;
}

[Bug c++/53506] Variadic templates in combination with function pointer problem

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53506

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-05-28 09:31:33 UTC ---
4.6 only rejects the first one:

t.cc: In function 'int main()':
t.cc:17:18: error: no matching function for call to 'A<int>::a(int (&)(int,
int), int)'
t.cc:17:18: note: candidate is:
t.cc:5:3: note: template<class RES, class ... FARGS> static void A::a(RES
(*)(FARGS ..., SARGS ...), FARGS ...) [with RES = RES, FARGS = {FARGS ...},
SARGS = {int}]

[Bug c++/53506] Variadic templates in combination with function pointer problem

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53506

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |66670
           Keywords|                            |rejects-valid
   Last reconfirmed|2017-08-20 00:00:00         |2021-7-27

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note I do think the code is valid , some of this is recorded as PR 66670.

Looks like clang cannot deduce return type still.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66670
[Bug 66670] "template argument deduction/substitution failed" with function
pointers and multiple parameter packs