C++ language feature to simplify naming types (especially in function declarations)

Question

I am wondering if there is a macro or language element in C++ that represents the same type as the return value in a function.

For example:

std::vector<int> Myclass::CountToThree() const
{
  std::vector<int> col;
  col.push_back(1);
  col.push_back(2);
  col.push_back(3);
  return col;
}

Instead of line std::vector<int> col; is there some sort of language element? I know it is pretty trivial but I am just bored with typing it ;-).

Answer 1

You can do two things:

1. Type aliasing, either using or typedef.

   typedef std::vector<int> IntVector;
   using IntVector = std::vector<int>;
   

   These two declarations are equivalent, and provide another name that compiler treats as a synonym of the original name. It can be used for templates as well.

   Why two notations, not just one? The using keyword was provided in C++11 to simplify notation for typedefs in templates.

2. In C++14, you could use the auto keyword for automatic return type deduction:

   auto Myclass::CountToThree() const
   {
       std::vector<int> col;
       col.push_back(1);
       col.push_back(2);
       col.push_back(3);
       return col;
   }
   

   For a broader explanation see this related question.

Answer 2

For your example, you could just write

std::vector<int> Myclass::CountToThree() const
{
    return {1,2,3};
}

In general, you can get the return type of a function with decltype, but this probably doesn't help in your situation:

std::vector<int> Myclass::CountToThree() const
{
  decltype( CountToThree() ) col;
  col.push_back(1);
  col.push_back(2);
  col.push_back(3);
  return col;
}