How can I create a new primitive type using C++11 style strong typedefs?

Question

I\'m trying to emulate in C++ a distinct type from the Nim programming language. The following example won\'t compile in Nim because the compiler catches the variables

Answer 1

Not sure this is what you want, it is ugly, but it works :) You can wrap the type into a template class,

template  // N is used for tagging
struct strong_typedef
{
    using strong_type = strong_typedef; // typedef for the strong type
    using type = T; // the wrapped type
    T value; // the  wrapped value

    strong_typedef(T val): value(val){}; // constructor
    strong_typedef(){value={};}; // default, zero-initialization

    // operator overloading, basic example: 
    strong_type& operator+(const strong_type& rhs)
    {
        value+=rhs.value; 
        return *this;
    }

    // display it
    friend ostream& operator<<(ostream & lhs, const strong_typedef& rhs)
    {
        lhs << rhs.value;
        return lhs;
    }
};

then use it as

// these are all different types
strong_typedef x = 1.1; 
strong_typedef y = 2.2;
strong_typedef z = 3.3;

std::cout << x + x << std::endl; // outputs 2.2, can add x and x
// cout << x + y << endl; // compile-time ERROR, different types

x, y and z are 3 different types now, because of the different N-s used in the template. You can access the type and value using the fields type and value, like x::value (will be double 1.1). Of course if you directly typedef the struct_typedef::type, you're back to square one, as you are losing the strong type. So basically your type should be strong_typedef and not strong_typedef::type.