Flexibility of template alias in C++0x

Question

As I understand, template aliases in C++0x will allow us to do the following:

template 
using Dictionary = std::map< std::string, T >;

D         


        

Answer 1

The syntax is:

template <typename Iter>
using ValueType = typename std::iterator_traits<Iter>::value_type;

as with your second one.

Source: http://www2.research.att.com/~bs/C++0xFAQ.html#template-alias

Their example is:

template<int N>
    using int_exact = typename int_exact_traits<N>::type;  // define alias for convenient notation

Answer 2

typename is required when a member type follows the :: operator and a template-id precedes it.

The usage of typename you mention isn't specific to template aliases nor is it required unless you're aliasing to a member such as ::type, but that is a common use case.

For example, there's no typename when introducing a simple alias name to an existing template.

template< typename x >
class bar;

template< typename x >
using foo = bar< x >; // no typename needed