Re: c++/10437: "using namespace" at global scope creates incorrect code

[Dean Foster <foster at diskworld dot wharton dot upenn dot edu>]

Sorry about forcing you to do more of the reduction.  I did at least
remove several 1000 lines of code!  But, every time I tried reducing
it further, I ended up removing the problem.  Thanks.

I'm willing to agree that that I've have an error/ambiguity in my
code.  But I don't understand why bringing in a namespace that isn't
being called should change the ambiguity status.  In other
words,

		main()
		{
		  using namespace foo;
		  /* ... */           // no error
		}
doesn't generate an error.  Neither does:

		main()
		{
		  /* ... */          // no error
		}

But, the following does generate an error:
		  
		using namespace foo;
		main()
		{
		  /* ... */         // generates error
		}

It seems that the first and the 3rd should be the same.  So maybe the
problem is that the third one is correct and that the first two should
catch the ambigity?  Or is my understanding of namespaces incorrect?


later,

dean


=============================================================================
Dean Foster                                                   dean at foster dot net
Statistics, Wharton, U. Penn                                     215 898 8233
Philadelphia PA 19104-6340                 http://diskworld.wharton.upenn.edu


> Date: 21 Apr 2003 15:06:07 -0000
> From: bangerth at dealii dot org
> Reply-To: bangerth at dealii dot org, dean at foster dot net, gcc-bugs at gcc dot gnu dot org,
>   gcc-prs at gcc dot gnu dot org, nobody at gcc dot gnu dot org, gcc-gnats at gcc dot gnu dot org
> X-SBRule: Spammy To: Header
> X-SBRule: Other Spammy Headers
> 
> Synopsis: "using namespace" at global scope creates incorrect code
> 
> State-Changed-From-To: open->closed
> State-Changed-By: bangerth
> State-Changed-When: Mon Apr 21 15:06:06 2003
> State-Changed-Why:
>     I don't think this is a bug. After quite some reducing,
>     your code looks like this:
>     ---------------------------
>     struct X {
>         int operator-(const X& it);
>     };
>     
>     template <class T>
>     struct Y {
>         typedef typename T::SOME_TYPE SOME_TYPE;
>         typedef int type;
>     };
>     
>     #ifdef BUG
>     template <class T> typename Y<T>::type operator-(T,T);
>     #endif
>     
>     int x = X() - X();
>     -----------------------------
>     (I replaced your using directive by the conditional
>     statement -- both just bring into visibility the
>     operator-.)
>     
>     What happens is that in the minus statement (which was
>     inside a std:: function in your example), both possible
>     operator- are considered, i.e. the member function and
>     the global one. The global one requires instantiation
>     of Y, at which point we realize that X::SOME_TYPE does
>     not exist:
>     g/x> /home/bangerth/bin/gcc-3.4-pre/bin/c++ -c x.cc -DBUG
>     x.cc: In instantiation of `Y<X>':
>     x.cc:15:   instantiated from here
>     x.cc:7: error: no type named `SOME_TYPE' in `struct X'
>     
>     Tracing back where this happens in your code is a little
>     more complicated, but I guess this is what happens -- you
>     try to use __gnu_cxx::normal_iterator::const_iterator
>     when bringing into scope the function in the namespace,
>     but this const_iterator doesn't exist.
>     
>     Wolfgang
> 
> http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10437
>