[Bug c++/17289] New: covariant returns and recursive templates don't mix

[Bug c++/17289] New: covariant returns and recursive templates don't mix

[jens dot maurer at gmx dot net]

This program:


struct Base
{
  virtual Base * clone() const = 0;
};

template<class F>
struct D : public Base
{
  F * clone() const { return 0; }
};

struct D2 : public D<D2>
{
};

D2 x;


results in this error:

covariant-return-recursive-tmpl.cc: In instantiation of `D<D2>':
covariant-return-recursive-tmpl.cc:13:   instantiated from here
covariant-return-recursive-tmpl.cc:9: error: invalid covariant return type for
`F* D<F>::clone() const [with F = D2]'
covariant-return-recursive-tmpl.cc:3: error:   overriding `virtual Base*
Base::clone() const'


Since D2 is (indirectly) derived from B, this error seems incorrect.

-- 
           Summary: covariant returns and recursive templates don't mix
           Product: gcc
           Version: 3.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jens dot maurer at gmx dot net
                CC: Jens dot Maurer at is-teledata dot com,gcc-bugs at gcc
                    dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17289

[Bug c++/17289] covariant returns and recursive templates don't mix

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-09-02 16:24 -------
Actually the error is correct.

Class D2 is not finished when you the template D<D2> is instantiated so we (the compiler) don't know 
that D2 is a derived class of Base.

Here is the error which ICC gives:
pr17289.cc(10): error: return type is not identical to nor covariant with return type "Base *" of 
overridden virtual function function "Base::clone"
    F * clone() const { return 0; }
        ^ 
          detected during instantiation of class "D<F> [with F=D2]" at line 13

pr17289.cc(17): error: object of abstract class type "D2" is not allowed:
            pure virtual function "Base::clone" has no overrider
  D2 x;
     ^

compilation aborted for pr17289.cc (code 2)

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17289