[Bug c++/55908] New: Problem binding a const member function to a const object

[Bug c++/55908] New: Problem binding a const member function to a const object

[sefi@s-e-f-i.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55908

             Bug #: 55908
           Summary: Problem binding a const member function to a const
                    object
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: sefi@s-e-f-i.de


The following code fails to compile:

#include <functional>

typedef std::function<void (int) >func;

struct foo
{
        void f(int) const
        {
        }

        void g() const
        {
                func(std::bind(&foo::f, this, std::placeholders::_1));
        }
};

int main()
{
}

g++-4.8.0-alpha20130106 -std=c++11 test.cpp

test.cpp: In member function 'void foo::g() const':
test.cpp:14:55: error: no matching function for call to
'std::function<void(int)>::function(std::_Bind_helper<false, void
(foo::*)(int)const, const foo* const, const std::_Placeholder<1>&>::type)'
   func(std::bind(&foo::f, this, std::placeholders::_1));
                                                       ^
test.cpp:14:55: note: candidates are:
In file included from test.cpp:1:0:
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2252:2:
note: template<class _Functor, class> std::function<_Res(_ArgTypes
...)>::function(_Functor)
  function(_Functor);
  ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2252:2:
note:   template argument deduction/substitution failed:
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2227:7:
note: std::function<_Res(_ArgTypes ...)>::function(std::function<_Res(_ArgTypes
...)>&&) [with _Res = void; _ArgTypes = {int}]
       function(function&& __x) : _Function_base()
       ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2227:7:
note:   no known conversion for argument 1 from 'std::_Bind_helper<false, void
(foo::*)(int)const, const foo* const, const std::_Placeholder<1>&>::type {aka
std::_Bind<std::_Mem_fn<void (foo::*)(int)const>(const foo*,
std::_Placeholder<1>)>}' to 'std::function<void(int)>&&'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2430:5:
note: std::function<_Res(_ArgTypes ...)>::function(const
std::function<_Res(_ArgTypes ...)>&) [with _Res = void; _ArgTypes = {int}]
     function<_Res(_ArgTypes...)>::
     ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2430:5:
note:   no known conversion for argument 1 from 'std::_Bind_helper<false, void
(foo::*)(int)const, const foo* const, const std::_Placeholder<1>&>::type {aka
std::_Bind<std::_Mem_fn<void (foo::*)(int)const>(const foo*,
std::_Placeholder<1>)>}' to 'const std::function<void(int)>&'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2207:7:
note: std::function<_Res(_ArgTypes ...)>::function(std::nullptr_t) [with _Res =
void; _ArgTypes = {int}; std::nullptr_t = std::nullptr_t]
       function(nullptr_t) noexcept
       ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2207:7:
note:   no known conversion for argument 1 from 'std::_Bind_helper<false, void
(foo::*)(int)const, const foo* const, const std::_Placeholder<1>&>::type {aka
std::_Bind<std::_Mem_fn<void (foo::*)(int)const>(const foo*,
std::_Placeholder<1>)>}' to 'std::nullptr_t'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2200:7:
note: std::function<_Res(_ArgTypes ...)>::function() [with _Res = void;
_ArgTypes = {int}]
       function() noexcept
       ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0-alpha20130106/include/g++-v4/functional:2200:7:
note:   candidate expects 0 arguments, 1 provided


The problem goes away if the int parameter is taken out, or if g() is not
const.
gcc-4.7.2 accepts the test case.

[Bug c++/55908] Problem binding a const member function to a const object

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55908

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2013-01-08
         AssignedTo|unassigned at gcc dot       |redi at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-08 13:33:56 UTC ---
Reduced:

#include <functional>

struct foo
{
        void f(int) const
        {
        }

        void g() const
        {
            auto mf = std::mem_fn(&foo::f);
            mf(this, 1);
        }
};

[Bug c++/55908] [4.8 Regression] Problem binding a const member function to a const object

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55908

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.7.3
   Target Milestone|---                         |4.8.0
            Summary|Problem binding a const     |[4.8 Regression] Problem
                   |member function to a const  |binding a const member
                   |object                      |function to a const object

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-08 13:35:18 UTC ---
Will fix it later today.

[Bug c++/55908] [4.8 Regression] Problem binding a const member function to a const object

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55908

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-08 21:01:23 UTC ---
Author: redi
Date: Tue Jan  8 21:01:14 2013
New Revision: 195035

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195035
Log:
    PR libstdc++/55908
    * include/std/functional (_Mem_fn::operator()): Fix constraints to
    avoid ambiguity.
    * testsuite/20_util/function_objects/mem_fn/55908.cc: New.
    * testsuite/20_util/bind/ref_neg.cc: Adjust dg-error line numbers.

Added:
    trunk/libstdc++-v3/testsuite/20_util/function_objects/mem_fn/55908.cc
Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/std/functional
    trunk/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc

[Bug c++/55908] [4.8 Regression] Problem binding a const member function to a const object

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55908

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-08 21:03:57 UTC ---
Fixed, thanks for the report.