#include <string>
namespace N {
  struct X { static std::string s(); };
}
namespace N {
  inline std::string ::N::X::s() { return ""; }
}
int main() {}

compiled with version 3.4.3 or 4.0.2 yields
GCC_Fehler_25022006.cpp:6: error: &#8216;struct std::string::N&#8217; has not been declared
GCC_Fehler_25022006.cpp:6: error: ISO C++ forbids declaration of &#8216;s&#8217; with no type
GCC_Fehler_25022006.cpp: In function &#8216;int N::s()&#8217;:
GCC_Fehler_25022006.cpp:6: error: invalid conversion from &#8216;const char*&#8217; to &#8216;int&#8217;

But I believe the above code is correct. Changing ::N::X::s() to N::X::s()
makes the code compile.