C++1y/C++14: Variable Template Specialization?

Question

According to C++1y/C++14 N3690, does the type of a variable template specialization have to be the same as the type of the primary template?

template

        

Answer 1

It's a bit risky to extrapolate that Clang is expressing the feature intended for standardization. (NB: I didn't refer to anything for this answer.)

Of course the fallout from allowing a change of type is that you can't specialize the template after it's been referenced in any way, whereas for all other kinds of templates the cutoff time is at ODR-use. Unless they're planning something wacky, this looks like a Clang bug.

You can always use a type template to declare the type of the variable template.

template< typename t >
struct x_type { typedef … type; };

template< typename t >
typename x_type< t >::type x = …;

Now x_type may be specialized. This just guards against the possibility that Clang is currently buggy. It doesn't allow you to refer to an object of indeterminate type. C++ just doesn't support that. Referring to the object ODR-uses the class template specialization.