[Bug c++/52768] New: Unable to get pointer to template function

[Bug c++/52768] New: Unable to get pointer to template function

[kmakaron11 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52768

             Bug #: 52768
           Summary: Unable to get pointer to template function
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: kmakaron11@gmail.com


GCC 4.6.3, as well as GCC 4.8 cannot resolve template method, even if it is
explicitly instantiated.
The code to explain the problem is:

template <class T>
struct Creator
{
    template <typename...Ts>
    static std::shared_ptr<T> create(Ts&&... vs)
    {
        std::shared_ptr<T> t(new T(std::forward<Ts>(vs)...));
        return t;
    }
};

class Car:
        public Creator<Car>
{
    private:
        friend class Creator<Car>;
        Car()
        {
        }
};

int main()
{
    std::function< std::shared_ptr<Car> () > createFn=&Car::create<>;

    return 0;
}

This results in following compiler error:
error: conversion from ‘<unresolved overloaded function type>’
       to non-scalar type ‘std::function<std::shared_ptr<Car>()>’ requested

However it compiles fine on Clang3.0 and 3.1.

[Bug c++/52768] Unable to get pointer to template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52768

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-03-29 13:02:14 UTC ---
(In reply to comment #0)
> The code to explain the problem is:

No it isn't, it's missing several include files.  I know it's "obvious" which
ones they are, but if five different people all look at the bug report and try
to reproduce the behaviour then they all have to figure it out and modify the
code.  You'd save everyone time by providing a *complete* testcase, as clearly
requested by the bug submissions guidelines.

A complete example would be:

template<typename Res>
struct function
{
    template<typename F> function(F) { }
};

template <class T>
struct Creator
{
    template <typename...Ts>
    static T* create(Ts&&... vs)
    {
        return new T(vs...);
    }
};

class Car:
        public Creator<Car>
{
    private:
        friend class Creator<Car>;
        Car() { }
};

int main()
{
    function< Car* () > createFn=&Car::create<>;
}

[Bug c++/52768] cannot resolve address of function template with empty template argument list

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52768

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-03-29
            Summary|Unable to get pointer to    |cannot resolve address of
                   |template function           |function template with
                   |                            |empty template argument
                   |                            |list
     Ever Confirmed|0                           |1

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-03-29 13:09:10 UTC ---
Same problem using a default template argument instead of a parameter pack:

template<typename Res>
struct function
{
    template<typename F> function(F) { }
};

template <class T>
struct Creator
{
    template <typename Ts = int>
    static T* create(Ts vs)
    {
        return new T(vs);
    }
};

class Car:
        public Creator<Car>
{
    private:
        friend class Creator<Car>;
        Car(int) { }
};

int main()
{
    function< Car* () > createFn=&Car::create<>;
}

(technically this is a C++11 bug, but G++ supports variadic templates and
default template arguments for functions in c++98 mode)

[Bug c++/52768] cannot resolve address of function template with empty template argument list

[kmakaron11 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52768

--- Comment #3 from kmakaron11 at gmail dot com 2012-03-29 13:25:11 UTC ---
I am sorry, Jonathan Wakely. This is my first GCC bug report.
Next time I will, try to put the fallout to minimum.

[Bug c++/52768] cannot resolve address of function template with empty template argument list

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52768

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-03-29 13:30:28 UTC ---
Even more reason to read http://gcc.gnu.org/bugs/ first then :)

[Bug c++/52768] cannot resolve address of function template with empty template argument list

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52768

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
      Known to work|                            |4.8.0, 4.9.0
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.8.0

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This is fixed in 4.8.0.