template method and default template argument - c++

Question

My problem can be resumed by the following piece of code:
template <typename T> struct C2;
template <typename T>
struct C1
{
template <typename Type,
template <typename Ti> class Container = C2>
void m() {}
};
template <typename T>
struct C2
{
template <typename Type = int,
template <typename Ti> class Container = C2> // <-- Here is the problem!
void m() {}
};
The gnu compiler, version 4.8.1 fails with the following message:
test-temp.C:16:47: error: invalid use of type ‘C2<T>’ as a default value for a template template-parameter
template <typename Ti> class Container = C2>
It refers to default template parameter C2 for the the method C2::m.
Apparently (it is my opinion), the compiler is seeing C2<T> as default parameter instead of C2 (without <T>). So, when it finds the instruction it fails because type C2<T> does not match with Container.
However, clang++, just for exactly the same code, compiles fine!
My questions:
Which compiler has the truth?
Is there some alternative for expressing the same sense with the current version of gnu compiler?
Thanks in advance
Leandro

Answer 1

I think Clang is correct, and g++ is in error, quote from the draft Standard (bold emphasis is mine)
14.6.1 Locally declared names [temp.local]
1 Like normal (non-template) classes, class templates have an
injected-class-name (Clause 9). The injectedclass-name can be used as
a template-name or a type-name. When it is used with a
template-argument-list, as a template-argument for a template
template-parameter, or as the final identifier in the
elaborated-typespecifier of a friend class template declaration, it
refers to the class template itself. Otherwise, it is equivalent to
the template-name followed by the template-parameters of the class
template enclosed in <>.
You can use the :: scope resolution operator to beat g++ into submission
template <typename T>
struct C2
{
template <typename Type = int,
template <typename Ti> class Container = ::C2>
// ^^ <-- here is the solution!
void m() {}
};
Live Example.

Answer 2

So does the 14.6.1 reference in TemplateRex's answer mean that G++ is correct (and Clang and VC++ are wrong) to accept this, since it uses X as the template argument to a template template parameter?
template< template< typename > class T >
class factory { };
template< typename T >
class X
{
friend class factory< X >; // ***
};
int main()
{
}
In this example G++ treats X as the name of the class template, whereas Clang and VC++ treat it as the injected class name.
Edit: Clang 5.0.0 now accepts the code, the same as G++ and EDG.