Does C# just copy field data on assigning to another field or refers to the data?

Question

At assigning one field to another, does the C# just copy data over, or actually creates link? In this article there's an example of game engine structure. The coder there has components contain their parent. In C#, do they just contain the parent copy, or they refer to it?

Example code:

class World
{
    ...
    public void Update()
    {
        ...
        ent.OnAttach(this);
        ...
    }
    ...
}

class Entity
{
    ...
    public void OnAttach(World world)
    {
        world_ = world;
    }
    ...
}

Could the Entity object now access World object and have access to it's fields and methods, like in the artice? (or I misunderstood the code?)

Answer 1

Because your data type World is defined as a class and not a struct that means that when you assign a variable of that type, only a reference to the same data is copied.

In other wrods, whether you then use world.SomeProperty = something or world_.someProperty = something they will be editing the same object in memory.

If you change your data type to be a struct then the entire data structure will be copied and you will have two copies of the same data.

Regardless of how you defined your data, once you have a reference to the data you can then access its methods or properties. So, yes, once your Entity object has a reference to the world object it can access any methods or properties on it (as long as they are not private).