[Bug c++/43117] New: Accepts invalid typedef

[bangerth at gmail dot com]

This is the remaining part of PR 9990 that concerns interpretation of
the core language rules. Consider this code snippet:
-----------------------------
struct B                           { typedef int type; };
template <typename T> struct D : B {
   typedef typename D::type type;
};

D<char> cc;
D<char>::type tcc;
-----------------------------
All GCC versions accept this. The question is whether the typedef in D is
well-formed: does D::type refer to the typedef in the base class, or to the
typedef we are currently declaring?

The issue is confusing because if D is not a template, like here:
-----------------------------
struct B     { typedef int type; };
struct D : B {
   typedef typename D::type type;
};

D<char> cc;
D<char>::type tcc;
-----------------------------
then apparently the code is ill-formed:

tmp> c++ -c a.cc
a.cc:3: error: using 'typename' outside of template
a.cc:6: error: 'D' is not a template
a.cc:7: error: 'D' is not a template
a.cc:7: error: expected initializer before 'tcc'

It is at best confusing that templates and non-templates should behave
differently in this regard.

I don't claim to know whether the current behavior is correct. Putting
this issue into a separate PR cleans up PR 9990, however.

Best
 W.


-- 
           Summary: Accepts invalid typedef
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bangerth at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43117