[Bug c++/39321] New: G++ remove cv qualifiers from typedefs during template instantiation

[Bug c++/39321] New: G++ remove cv qualifiers from typedefs during template instantiation

[dodji at gcc dot gnu dot org]

The following program should compile, but current g++ from trunk compiles it.

Please read the comments in the code:

~=~

template<typename T>
struct do_typedef
{
  typedef T type;
};


template<typename T> struct is_function;

// Let's name this template partial specialization #1
template<typename T>
struct is_function< T ()>
{ 
};

template<typename T> struct is_member_func;

template<typename T, typename C>
struct is_member_func<T C::*>
{
  //[1] okay, the following line should not compile. Here is why.  
  //After the type substitution that happens at instantiation time,
  //the value of the argument that matches the T parameter is
  //'void () () const'.
  //In that context, the result of the substitution of T in the expression
  //do_typedef<T>::type _should_ be 'void () () const' as well.
  //So will be the argument of the is_function template.
  //'void () () const' is not compatible with 'T ()', so the  
  //partial template specialization #1 should be instantiated.
  //So we should get a compilation error.
  is_function<typename do_typedef<T>::type> t;
};


struct A;

// Should not compile because of the comment [1] above.
is_member_func<void (A::*) (void) const> t;
~=~

What happens is that during the type substitution of
do_typedef<T>::type, g++ removes the const qualifier from the 'void () ()
const' function. And that is a bug.

I'll attach below a patch that fixes it.


-- 
           Summary: G++ remove cv qualifiers from typedefs during template
                    instantiation
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dodji at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39321

[Bug c++/39321] G++ remove cv qualifiers from typedefs during template instantiation

[dodji at gcc dot gnu dot org]

------- Comment #1 from dodji at gcc dot gnu dot org  2009-02-27 20:06 -------
Created an attachment (id=17372)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17372&action=view)
Don't remove cv quals from typedefs during type substitution


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39321

[Bug c++/39321] G++ remove cv qualifiers from typedefs during template instantiation

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2009-02-28 08:09 -------
This is related to bug 37806.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39321

[Bug c++/39321] G++ remove cv qualifiers from typedefs during template instantiation

[jason at gcc dot gnu dot org]

------- Comment #3 from jason at gcc dot gnu dot org  2009-03-02 01:22 -------
Yep, duplicate.

*** This bug has been marked as a duplicate of 37806 ***


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39321