Operations on arbitrary value types

Question

This article describes a way, in C#, to allow the addition of arbitrary value types which have a + operator defined for them. In essence it allows the following code:

public T Add(T val1, T val2)
{
   return val1 + val2;
}

This code does not compile as there is no guarantee that the T type has a definition for the '+' operator, but the effect is achieved with code like this:

public T Add(T val1, T val2)
{
   //Num<T> defines a '+' operation which returns a value of type T
   return (new Num<T>(val1) + new Num<T>(val2));
}

Follow the link to see how the Num class achieves this. Anyways, on to the question. Is there any way to achieve the same effect in C or C++? For the curious, the problem I'm trying to solve is to allow a CUDA kernel to be more flexible/general by allowing it to operate on more types.

Update: For .NET, Marc Gravell has made a utility library which solves the operator problem very elegantly.

Answer 1

Due to the way templates are compiled in C++, simply doing:

template < class T >
T add(T const & val1, T const & val2)
{
    return val1 + val2;
}

will work, you'll get a compile error for every type where an operator+ is not defined.

C++ templates generate code for every type instantiation, so for every type T code will be generated that does the right thing. This way C++ doesn't need Num<> trickery.

In plain C, this is not possible as far as I know.

Answer 2

In C++ this is simply not an issue. The code as in your first sample works if literally translated into C++ (ETA: as Pieter did), but I can't think of any situation where directly using + wouldn't work. You're looking for a solution to a problem that doesn't exist.

Answer 3

This can easily be done in C++ using templates:

template <typename T>
T Add(T val1, T val2)
{
  return val1 + val2;
}

Note, however, that this must be defined in a header file, and you probably also want to pass the parameters by const reference instead of by value.

This cannot be done in plain C at all.

Answer 4

It can be done in C as well, although I'm not sure it meets the problem requirements, with a Macro.

#define ADD(A,B) (A+B)

Answer 5

Templates in C++. In C, not without massive hassle and overhead.

template<typename T> 
T add(T x, T y)
{ 
    return x + y;
}