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From: "schaub.johannes at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/56190] New: GCC fails deducing a "void(*)(int, float, double)" to a "void(*)(T..., float, double)" with T={int}
Date: Sun, 03 Feb 2013 13:57:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56190

             Bug #: 56190
           Summary: GCC fails deducing a "void(*)(int, float, double)" to
                    a "void(*)(T..., float, double)" with T={int}
    Classification: Unclassified
           Product: gcc
           Version: 4.7.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: schaub.johannes@googlemail.com


From
http://stackoverflow.com/questions/14664589/variadic-template-code-compiles-on-gcc-4-6-but-not-on-clang-or-gcc-4-7
:

class Test {
    public:
    template <class... A2> void print (void(*function)(A2..., float, double)) {

    }
};

void test_print (int a, float b, double c) { }

int main () {
    Test test;
    test.print<int> (&test_print);
}

Fails with

source.cpp:14:33: note: candidate is:
source.cpp:3:33: note: template<class ... A2> void Test::print(void (*)(A2 ...,
float, double))
source.cpp:3:33: note:   template argument deduction/substitution failed:
source.cpp:14:33: note:   mismatched types 'float' and 'int'

GCC does apparently not substitute the explicitly specified arguments of "A2"
before attempting the argument deduction.