Create type copies

Question

How do you create type copies? For example, how do I create types Mass, Acceleration and Force which are not implicitly convertible to double(or any other numeric type), but otherwise have all the characteristics of a double. This would allow a compile-time input validity check for this function:

Force GetForceNeeded(Mass m, Acceleration a);

ensuring that GetForceNeeded can only be called with arguments of type Mass and Acceleration.

Of course, I could achieve this by manually creating a copy of the type:

class Force final
{
public:
//overload all operators
private:
double value;
};

but this is cumbersome. Is there a generic solution?

Answer 1

As many commentators have pointed out, one solution is to use BOOST_STRONG_TYPEDEF which provides all the features requested in the question. And here's example usage from their docs:

#include <boost/serialization/strong_typedef.hpp>


BOOST_STRONG_TYPEDEF(int, a)
void f(int x);  // (1) function to handle simple integers
void f(a x);    // (2) special function to handle integers of type a 
int main(){
    int x = 1;
    a y;
    y = x;      // other operations permitted as a is converted as necessary
    f(x);       // chooses (1)
    f(y);       // chooses (2)
}    typedef int a;

There is a proposal to add opaque typedefs to C++1y.

(I am leaving this answer as I can't find an exact dupe. Please flag if that isn't the case.)