[Bug c++/43608] Boost.MPL code doesn't get the placeholders substituted anymore

["jason at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #5 from jason at gcc dot gnu dot org  2010-04-01 14:47 -------
My copy of EDG 4.1 does not accept the reduced testcase; it gives the same
error as GCC 4.5.

"red.cc", line 111: error: class "arg<2>" has no member "inner_type"
          typedef typename Foo::inner_type type;
                                ^
          detected during:
            instantiation of class "metafunction<Foo> [with Foo=arg<2>]" at
                      line 83
            instantiation of class "template_arity_impl<F, N> [with
                      F=metafunction<arg<2>>, N=1]" at line 91
            instantiation of class
                      "template_arity<F> [with F=metafunction<arg<2>>]" at
                      line 116

We instantiate metafunction<arg<2>> for argument-dependent lookup of the call
to arity_helper(type_wrapper<F>).  3.4.2 says that if an argument type is a
class template specialization, we consider the associated classes and
namespaces of the template arguments, which in this case means F, or
metafunction<arg<2>>.  And in order to perform that lookup, we instantiate
metafunction<arg<2>>.

Providing the explicit specialization prevents the implicit instantiation, so
argument-dependent lookup just doesn't consider that scope.  This is also fully
conformant.


-- 

jason at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43608