[Bug c++/24893] New: inherited polymorphic template class

[Bug c++/24893] New: inherited polymorphic template class

[fmaerten at igeoss dot com]

Hi all,

  We just found a bug while compiling the following code. The derived template
class doens't know the pure virtual method from its parent class when this
template class has a method with the same name, but with different arguments:

class A {
public:
  virtual void doit() = 0 ;
} ;

template <typename T>
class B: public A {
public:
  virtual void doit(double) {}
} ;

class C: public B<double> {
public:
  virtual void doit() {}
} ;


int main() {
  A*         a = new C ;
  B<double>* b = new C ;
  a->doit() ; // ok

  // Compile error with gcc-3.4.3:
  //   error: no matching function for call to `B<double>::doit()'
  //   note: candidates are: void B<T>::doit(double) [with T = double]
  b->doit() ;
}


-- 
           Summary: inherited polymorphic template class
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: fmaerten at igeoss dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24893

[Bug c++/24893] inherited polymorphic template class

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2005-11-16 15:17 -------
First this has nothing to do with templates, you can reproduce the error
message without templates.
Second this is how C++ works.
doit(double) in B<T> hides doit(void) in A as it is the same name.
The way to fix it would either to do:
  b->A::doit() ;
or:
Change defintion of B to include a using statement like:
template <typename T>
class B: public A {
public:
  virtual void doit(double) {}
  using A::doit;
} ;

This makes both doit visible in B<T>.  In fact you will have the same issue
trying to call doit(double) in C, you solve it the same way.


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24893