Question

I wonder if and how writing “almighty” classes in c++ actually impacts performance.

If I have for example, a class Point, with only uint x; uint y; as data, and have defined virtually everything that math can do to a point as methods. Some of those methods might be huge. (copy-)constructors do nothing more than initializing the two data members.

class Point
{
   int mx; int my;
   Point(int x, int y):mx(x),my(y){};
   Point(const Point& other):mx(other.x),my(other.y){};
 // .... HUGE number of methods....
};

Now. I load a big image and create a Point for every pixel, stuff em into a vector and use them. (say, all methods get called once)
This is only meant as a stupid example!

Would it be any slower than the same class without the methods but with a lot of utility functions? I am not talking about virtual functions in any way!

My Motivation for this: I often find myself writing nice and relatively powerful classes, but when I have to initialize/use a ton of them like in the example above, I get nervous.
I think I shouldn’t.

what I think I know is:

1. Methods exist only once in memory.
   (optimizations aside)
2. Allocation
   only takes place for the data
   members, and they are the only thing
   copied.

So it shouldn’t matter. Am I missing something?

Answer 1

You are right, methods only exist once in memory, they’re just like normal functions with an extra hidden this parameter.

And of course, only data members are taken in account for allocation, well, inheritance may introduce some extra ptrs for vptrs in the object size, but not a big deal