When a template-id refers to the specialization of an alias template, it is equivalent to the associated type obtained by substitution of its template-arguments for the template-parameters in the type-id of the alias template. [ Note: An alias template name is never deduced. — end note ] [ Example:
template<class T> struct Alloc { /* ... */ };
template<class T> using Vec = vector<T, Alloc<T>>;
Vec<int> v;
template<class T>
void process(Vec<T>& v)
{ /* ... */ }
template<class T>
void process(vector<T, Alloc<T>>& w)
{ /* ... */ }
template<template<class> class TT>
void f(TT<int>);
f(v);
template<template<class,class> class TT>
void g(TT<int, Alloc<int>>);
g(v);
— end example ]
However, if the template-id is dependent, subsequent template argument substitution still applies to the template-id. [ Example:
template<typename...> using void_t = void; template<typename T> void_t<typename T::foo> f(); f<int>();
— end example ]
The type-id in an alias template declaration shall not refer to the alias template being declared. The type produced by an alias template specialization shall not directly or indirectly make use of that specialization. [ Example:
template <class T> struct A;
template <class T> using B = typename A<T>::U;
template <class T> struct A {
typedef B<T> U;
};
B<short> b;
— end example ]
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