Question

I feel pretty ignorant asking this, but would someone be able to explain to me why this is happening?

class MyClass{ public int i {get; set; } }
class Program
{
    static void Main(string[] args)
    {
        MyClass a = new MyClass();
        MyClass b = new MyClass();

                b.i = 2;
        a = b;
        a.i = 1;

        Console.Write(b.i + "\n"); //Outputs 1
    }
}

This makes sense to me were I using pointers and all that great stuff, but I was under the impression that with C# that “b” would remain independent from “a.”

Am I just using some terribly bad practice? Maybe someone could point me towards something that explains why this is so in C#?

Thanks.

Answer 1

It’s this line that has you confused:

a = b;

You expected b to be copied to a by value, but in fact all that happens is you’ve assigned the reference from b to a.

.Net divides the world into two categories: reference types and value types (there’s also delegate types and a couple others, but that’s another story). Any class you define is a reference type, and there are a few important things to remember about reference types:

• There’s no built-in way to do a deep copy
• Be careful checking equality. == is intended for reference equality (do the variables refer to the same object) while .Equals() is intended for value equality, and you may need to override .Equals() (and GetHashCode()) for your type to get that right.
• assignment just copies the reference (this is the part that bit you)