[Bug libstdc++/48313] New: std::bind with template function

[Bug libstdc++/48313] New: std::bind with template function

[joerg.richter@pdv-fs.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

           Summary: std::bind with template function
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: joerg.richter@pdv-fs.de


$ cat > t.cc << EOF
#include <functional>

template<class T> void func( T )
{}

int main( int, char** )
{
  std::bind( func<int>, 0 );
}
EOF

$ g++ t.cc -std=gnu++0x
t.cc: In function 'int main(int, char**)':
t.cc:8:27: error: cannot bind 'void(int)' lvalue to 'void (&&)(int)'
...

This is with GCC 4.6.0.  This works with GCC 4.5.2.

[Bug libstdc++/48313] std::bind with template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.03.28 12:17:25
     Ever Confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-03-28 12:17:25 UTC ---
The example should work. I'm travelling today but will check the <functional>
code later to see why the F&& constructor is being chosen instead of the const
F& one.

[Bug libstdc++/48313] std::bind with template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-03-28 12:24:23 UTC ---
The example can be modified to work by passing a pointer, so the template
argument isn't deduced as a function type:

  std::bind( &func<int>, 0 );

[Bug libstdc++/48313] std::bind with template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-03-28 12:43:12 UTC ---
It's not the _Bind constructor, it's the bind() call itself, this demonstrates
the problem:

template<typename _Functor, typename... _ArgTypes>
    inline
    void
    bind(_Functor&& __f, _ArgTypes&&... __args) { }

template<class T> void func( T )
{}

int main( int, char** )
{
    bind( func<int>, 0 );
}


we might just need to overload std::bind for function types

std::bind() in 4.5 was defined differently as it didn't support rvalues
properly, so didn't show the problem

[Bug libstdc++/48313] std::bind with template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-03-28 14:26:35 UTC ---
slightly further reduced:


template<typename Functor, typename ArgTypes>
    inline void
    bind(Functor&& f, ArgTypes&& a) { }

template<typename T>
void func( T )
{}

int main( int, char** )
{
    bind( func<int>, 0 );
}

this is certainly not a libstdc++ bug (std::bind matches the signature require
by the C++0x draft)

I think the parameter is a non-deduced context, because the argument is an
overload set containing one or more function templates ([temp.deduct.call p6)

So I think this is actually invalid and G++ is right to reject it.

[Bug c++/48313] [C++0] std::bind with template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |UNCONFIRMED
                 CC|                            |jason at gcc dot gnu.org
          Component|libstdc++                   |c++
            Summary|std::bind with template     |[C++0] std::bind with
                   |function                    |template function
     Ever Confirmed|1                           |0

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-03-28 17:02:14 UTC ---
Actually no, that paragraph doesn't apply because P is a reference type not
function type.

Jason should the call to f(h<int>) be accepted here?

template<typename F>
void f(F&&) { }

void g() { }

template<typename T> void h() { }

int main()
{
  f( g );       // OK
  void (&p)() = h<int>;
  f( p );       // OK
  f( h<int> );  // ???
}

[Bug c++/48313] [C++0x] std::bind with template function

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|2011-03-28 12:17:25         |2011.03.28 20:10:59
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> 2011-03-28 20:10:59 UTC ---
Yes, that's a bug.

[Bug c++/48313] [C++0x] std::bind with template function

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> 2011-03-29 00:04:57 UTC ---
Author: jason
Date: Tue Mar 29 00:04:54 2011
New Revision: 171643

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=171643
Log:
    PR c++/48313
    * pt.c (maybe_adjust_types_for_deduction): Handle T&& deduction
    from overloaded function.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/rv-deduce2.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/48313] [C++0x] std::bind with template function

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> 2011-03-29 14:25:34 UTC ---
Author: jason
Date: Tue Mar 29 14:25:22 2011
New Revision: 171669

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=171669
Log:
    PR c++/48313
    * pt.c (maybe_adjust_types_for_deduction): Handle T&& deduction
    from overloaded function.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/cpp0x/rv-deduce2.C
Modified:
    branches/gcc-4_6-branch/gcc/cp/ChangeLog
    branches/gcc-4_6-branch/gcc/cp/pt.c
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog

[Bug c++/48313] [C++0x] std::bind with template function

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.1

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> 2011-03-29 14:30:17 UTC ---
Fixed for 4.6.1.

[Bug c++/48313] [C++0x] std::bind with template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48313

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-03-31 12:40:24 UTC ---
Thanks for the fix, Jason, I've just encountered the bug myself using
boost::thread

I expect others will to, so for the benefit of search engines, the error is

post_event_test.cc:130:47: error: cannot bind 'void()' lvalue to 'void (&&)()'
/home/jwakely/src/boost/boost_1_45_0/boost/thread/detail/thread.hpp:167:9:
error:   initializing argument 1 of 'boost::thread::thread(F&&) [with F =
void()]'