Ion Gaztañaga wrote: [...]
template<class Pointer> class container { Pointer ptr; public: void func() { static_pointer_cast<int>(Pointer()); } };
} //namespace dummy { } //namespace boost {
[...]
This code compiles in VC 7.1 and VC 8 but fails with gcc, complaining the "there is no declaration for static_pointer_cast". If we change the header order to:
#include "smart_ptr.h" #include "container.h" #include "container_factory.h"
This compiles fine because the static_pointer_cast definition is found before the call. My first question is:
* Is this gcc error correct? Revising a bit ADL + template issues (a fairly complicated logic that should be removed from C++, in my opinion) I think that gcc is right.
Questionable. The problem is that for static_pointer_cast<int> to be valid, static_pointer_cast must be known to be a template. It is understandable why g++ rejects it without a declaration, but I'm not sure whether this is conforming now, much less whether it'd be conforming tomorrow if there are open core issues for this case. Even if static_pointer_cast<int> is parsed correctly, I recall a core issue about whether the call should be subject to ADL.
* If gcc is correct, what is the implementor supposed to do? Every templatized class header shouldn't include smart_ptr.h because smart_ptr is unknown and it can even be a user-defined class.
To make the above work for raw pointers (these don't have an associated namespace), the implementor would need to #include boost/pointer_cast.hpp and add an using declaration for boost::static_pointer_cast. This may or may not make g++ happy.
I must have missed something, because otherwise, I would find ADL really useless as a robust customization point.
The typical ADL expression doesn't have an explicit <int> template parameter.