Making copies of a type
How do you create copies of types? For example, how do I create types Mass
, Acceleration
and Force
that are implicitly convertible to double
(or any other numeric type), but otherwise have all the characteristics of a double
. This will allow compile-time input validation for this function:
Force GetForceNeeded(Mass m, Acceleration a);
so that GetForceNeeded
you can only call with arguments like 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 general solution?
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As many commenters have pointed out, one solution is to use BOOST_STRONG_TYPEDEF , which provides all the functionality asked in the question. And here is a usage example 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 in C ++ 1y.
(I am leaving this answer because I cannot find the exact deception. Please note if this is not the case).
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