template alias error

[SSteven]

I have written the following code:

template<typename Val>
struct Forward
{
   /// ...
};

template<typename Val>
using Value_type<Forward<Val>> = Val;

However, I get the following compilation error on the last LoC:

error: expected '=' before '<' token|
error: expected type-specifier before '<' token|
error: expected unqualified-id before '<' token|

What is wrong with the LoC that includes the Value_type declaration?

This example is taken from Stroustrup's book.

Thanks.

[JLBorges]

template < typename T > struct Value_type { /* ... */ };

template< typename T > struct Forward { /* ... */ };

template< typename T > using Val = Value_type< Forward<T> > ;

static_assert( std::is_same< Val<int>, Value_type< Forward<int> > >::value, "unexpected" ) ;

[Cubbi]

clang gives a more sensible message: "error: partial specialization of alias templates is not permitted". This looks like a bug in the book: using a language feature that was going to, but didn't quite make it into the standard.