[Bug c++/24588] Fails to identify template using local classes

[bangerth at dealii dot org]

------- Comment #6 from bangerth at dealii dot org  2006-01-24 05:48 -------
(In reply to comment #5)
> Well, the actual argument type is wholely resolved at point of call. And the 
> formal parameter type is valid at the point where sort is defined. It will 
> recognize A<int> as an A<E>, it will recognize A<int>* as an A<E>*, and it
> should 
> (I think) recognize A<int>::iterator as an A<E>::iterator.

No, it can't. Here, E is in what is called a non-deducible context.

As an example of why it can't be deduced, consider an example like this:
---------------------
template <class E> class C {
  typedef int* iterator;
  iterator begin();
};

template <class E>
void f (const C<E>::iterator);

int main () {
  C<int> c;
  f(c.begin());
}
---------------

It would seem that the compiler should deduce E=int in the call to f(). 
However, it is worth realizing that types would also match for f<double>, and
in fact for every other choice of E as well.

In effect, E can't be deduced. The standard says so.

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at dealii dot org
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24588