Re: Type of template member functions.

From:
=?ISO-8859-1?Q?Elias_Salom=E3o_Helou_Neto?= <eshneto@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Tue, 9 Nov 2010 04:54:03 -0800 (PST)
Message-ID:
<5552c6df-7666-49c8-bd00-5e1aa73287f1@x7g2000prj.googlegroups.com>
On 8 nov, 20:39, "Johannes Schaub (litb)" <schaub-johan...@web.de>
wrote:

Elias Salom=E3o Helou Neto wrote:

Hello, the following program when compiled with GCC gives the output
that follows the listing:

#include <iostream>
#include <typeinfo>

struct A {
  template< unsigned n >
  void member( const double& );
};

int main()
{
  std::cout << typeid( void (A::*) ( const double& ) ).name() << '\n'=

;

  std::cout << typeid( &A::member< 0 > ).name() << '\n';
  std::cout << typeid( &A::member< 1 > ).name() << '\n';

  return( 0 );
}

Output:

M1AFvRKdE
PFvRKdE
PFvRKdE

Is that a GCC bug or the types of template member function and member
functions are not the same?


The type of "&A::member<0>" is of type "void(A::*)(const double&)" - a=

re

you sure that "member" in your code is not a static member function?
"PFvRKdE" is the mangled form for type "void (*)(double const&)".


Yes, I have realized that GCC treats template _member_ function as
static functions, but this is not the point. Even if I try to bind to
an ordinary function the test still does not work, see below.

However your question implies that you think that "&A::member_function"
would be of the type of the member function, but that's not quite the cas=

e.

Could you explain why? I did not mean to imply that.

It will be a pointer to member. Only "A::member_function" - not preceeded=

 by

& - will have the type of the member function, but that expression must
either be immediately followed by "()", or must unambiguously refer to a
static member function. In both cases, that expression would have the typ=

e

"void(const double&)", for the function type in your example.


Ok, now you've got the hole code:

#include <iostream>

template< class T >
class has_apply {

  typedef char yes[1];
  typedef char no[2];

  template< class U, U u >
  struct binder {};

  template< class U, unsigned n >
  static yes& test( U*,
                    binder< void (U::*) ( const double& ),
                            &U::template apply< n >
                          >* = 0
                  );

  template< class U, unsigned n >
  static yes& test( U*,
                    binder< void (U::*) ( const double& ) const,
                            &U::template apply< n >
                          >* = 0
                  );

  template< class U, unsigned n >
  static yes& test( U*,
                    binder< void (*) ( const double& ),
                            &U::template apply< n >
                          >* = 0
                  );

  template< class U, unsigned n >
  static yes& test( U*,
                    binder< void (U::*) ( double ),
                            &U::template apply< n >
                          >* = 0
                  );

  template< class U, unsigned n >
  static yes& test( U*,
                    binder< void (U::*) ( double ) const,
                            &U::template apply< n >
                          >* = 0
                  );

  template< class U, unsigned n >
  static yes& test( U*,
                    binder< void (*) ( double ),
                            &U::template apply< n >
                          >* = 0
                  );

  template< class U, unsigned n >
  static no& test( ... );

public:

  static const bool result = ( sizeof( yes ) == sizeof( test< T, 0u

( (T*)(0) ) ) );


};

class A {
public:
    template< unsigned n >
    void apply( const double& );

};

int main()
{
  std::cout << std::boolalpha << has_apply< A >::result << '\n';
  return( 0 );
}

Run:

$g++ -Wall -o test test.cpp&& ./test
false

As it appears you have a static member function, it's clear why this fail=

s.

So double check everything.


Your assumption is wrong, I do not have a static member function. Even
if I had, shouldn't the code above return true?

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