SFINAE and enable_if<>


Type alias, alias template

The keyword using is a another way of creating a typedef, an alias of a type.

template<typename T> class Vector {

    using value_type = T; // Same as: typedef T value_type;

Vector<int> v;
Vector<int>::value_type x = 10; // x is of type int.

using value_type = T; is equivalent to typedef T  value_type;. There is also a form of using for use with templates. It can help to create, for example, more readable templates.

template<class T> struct Alloc {

template<class T> using Vec = vector<T, Alloc<T>>; // type-id is vector<T, Alloc<T>>

Vec<int> v; // Vec<int> is the same as vector<int, Alloc<int>>

Vec is an alias template, and Vec<int> results in substituting int for T in template<typename T> vector<T, Alloc<T>>. Thus, Vec<int> is just an alias for vector<T, Alloc<T>>.


Finish later.