Non-member conversion functions; Casting different types, e.g. DirectX vector to OpenGL vector

Question

I am currently working on a game \"engine\" that needs to move values between a 3D engine, a physics engine and a scripting language. Since I need to apply vectors from the

Answer 1

I would suggest writing them as a pair of free functions (i.e. don't worry about making them 'operators'):

vector3d vector3dFromBt(const btVector3& src) {
    // convert and return
}

btVector3 btVectorFrom3d(const vector3d& src) {
    // convert and return
}

void f(void)
{
  vector3d one;   
// ...populate...   
  btVector3 two(btVectorFrom3d(one));    
// ...
  vector3d three(vector3dFromBt(two));
}