using keyword

Introduction

#include <iostream>
#include <vector>
#include <memory>

using namespace std ;

  // Alias template
  template <typename T>
  using MyVector = vector<T>;

  // Alias template for a custom smart pointer
  template <typename T>
  using MySmartPtr = unique_ptr<T>;



int main()
{
   // Traditional typedef
  typedef vector<int> IntVectorOld  ;

  // C++11 using for type alias
  using IntVectorNew = vector<int>   ;

  IntVectorOld v1 ; v1.push_back( 2 ) ;
  IntVectorNew v2 ; v2.push_back( 2 ) ;

  MyVector<int> v3 ; v3.push_back( 2 ) ;
  // Usage
  MySmartPtr<int> ptr_to_int( new int(10) )  ;
  MySmartPtr<double> ptr_to_double( new double(3.14)  )  ;


    return 0;
}

We had the "typedef" key word pre C++ 11 that lets us alias a type. There
is a new keyword "using" that can also alias types. From the above code:

  typedef vector<int> IntVectorOld  ;

  // C++11 using for type alias
  using IntVectorNew = vector<int>   ;

However "using" can also alias templates:

  template <typename T>
  using MyVector = vector<T>;

MyVector<int> v3 ; v3.push_back( 2 ) ;

We create an object of "MyVector" by supplying the
type "int" . The "MySmartPtr" works in a similar manner.