Re: template argument required

[Larry I Smith]

Patrick Rammelt wrote:
> Larry I Smith wrote:
>
> > Patrick Rammelt wrote:
> >
> > > Hi
> > >
> > > I have just upgraded from gcc-3.3.3 to gcc-4.0.0 Trying to compile some
> > > old code I stumbled over an error. I created this short example:
> > >
> > > -------------------- gcctest.cpp -----------------------------
> > > #include <iostream>
> > >
> > > using namespace ::std;
> > >
> > > template <class T>
> > > class A {
> > > public:
> > >
> > >   A (void) {}
> > >
> > >   template <class X>
> > >   class A& foo (X p) {         // no error without "class"
> > >     cout << "template foo\n";
> > >     return(*this);
> > >   }
> > >
> > > };
> > >
> > > int main (void) {
> > >
> > >   A<double> a1, a2;
> > >   a1.foo(a2);                  // line 22: error (see below)
> > >
> > >   exit(0);
> > > }
> > > --------------------------------------------------------------------
> > >
> > > no errors when compiling it with g++-3.3.3, but g++-4.0.0 (and 
> > > g++-3.4.1) complaints:
> > >
> > > gcctest.cpp: In function ‘int main()’:
> > > gcctest.cpp:22: error: template argument required for ‘struct A’
> > > gcctest.cpp:22: error: no matching function for call to
> > >                 ‘A<double>::foo(A<double>&)’
> > >
> > > Substituting "class A&" by just "A&" in foo it compiles without any 
> > > warnings or errors (and works as expected). Does this make any sense, 
> > > or is it a bug?
> >
> > The definition of foo() is ambiguous.
> > Does this fix it?
> >
> >    template <class X>
> >    class A<T> & foo (X p) {         // <-- specify WHICH type of 'A'
> >      cout << "template foo\n";
> >      return(*this);
> >    }
>
>
> Yes it does - Thanks! My fix was to leave away the "class", but this 
> solution looks better. It really _looks_ better because my editor 
> /needs/ the "class" for syntax-highlighting :-)
> I'm just curious: is there a reason why the keyword "class" makes a 
> difference here - or should there occure an error either in both cases 
> or not at all? At least I think the error-message (pointing to line 22) 
> is a bit misleading here?!
>
> Ciao,
> Patrick

'class' should not be required.  In fact, it may
confuse the issue (on some compilers).  Try:

  A<T> & foo (X p) {
    ...
  }

Regards,
Larry

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