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

[bangerth@dealii.org]

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