[Bug c++/24139] New: Forward declaration of class in template class

[mspencer at ndsuk dot com]

We have code that works with g++ 3.2.3 (i386-redhat-linux) that no longer works
on 4.

#include <iostream>
using namespace std;

template<typename T>
class Hide {
 public:

  Hide() {
        a=new Hidden();
  }

  class Hidden;

private:
  Hidden *a;
};

template<>
class Hide<int>::Hidden
{
 public:
  Hidden();
};

template<>
Hide<int>::Hidden::Hidden() {
  cout << "Hello from int->Hidden" << endl;
}

int main(int argc,char *argv[])
{
  Hide<int> b;
}

I get the error:
   error: template-id ‘Hidden<>’ for ‘Hide<int>::Hidden<int>::Hidden()’ does not
match any template declaration

However, if I remove the Hidden constructor from the code , I get the error:
   undefined reference to `Hide<int>::Hidden::Hidden()

I am confused by the Hidden<int> in the first example and think that the
undefined reference error is correct.

-- 
           Summary: Forward declaration of class in template class
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mspencer at ndsuk dot com
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: i386-redhat-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24139