David Abrahams wrote:
struct A { typedef int M;
template <class M> void foo(void) { M m; // which M is this? } };
I know the C++ committe is discussing this issue at this moment. The argument would be that "M" names the typedef because it's "more stable" than the template parameter (which could get renamed in an out-of-class definition). See also http://gcc.gnu.org/PR13967 for a detailed discussion.
I'm sorry, but that's insane from a usability POV. C++ already has too many places where something far away can be chosen instead of the "obvious" alternative close by (see ADL).
I'm not advocating that, I'm just saying that it's how GCC currently works and it seems to be a gray area of the standard. My personal opinion is that GCC is wrong: I agree with you that the template parameter should be found on name lookup.
Introducing a typedef in an enclosing namespace should not affect the meaning or well-formedness of a use of a template parameter, especially because this sort of thing is liable to happen due to changes in #includes.
We're not speaking of namespace scope but class scope, though. It's a bit harder to change things at class scope. Anyway, we both agree that it's insane for C++ to behave like this, so never mind :) -- Giovanni Bajo