Question

I’ve been playing around with c++ lately and wondered why there were so many global functions. Then I started thinking about programming in c# and how member functions are stored, so I guess my question is if I have a:

public class Foo {
    public void Bar() { ... }
}

and then I do something silly like adding 1,000,000 Foo’s to a list; does this mean I have 1,000,000 Foo objects sitting in memory each with there own Bar() function? Or does something much more clever happen?

Thanks.

Answer 1

Nope, there is only one instance. All instances of a class point to an object that contains all the instance methods that take an implicit first parameter affectionately called this. When you invoke an instance method on an instance the this pointer for that instance is passed as the first parameter to that method. That is how the method knows all the instance fields and properties for that instance.

For details see CLR via C#.

This is, of course, complicated by virtual methods. CLR via C# will spell out the distinction for you and is highly recommended if you are interested in this subject. Either way, there is still only one instance of each instance method. The issue is just how these methods are resolved.