Question

So I found out today that structs and classes act differently when used to assign to variables in C#.. It’s to my understanding that when I assign a struct to a variable, the variable stores a copy of that struct, and when I assign a class to a variable, the variable stores the reference to that class instance.

In this case, dad2 contains a copy of dad1, so shouldn’t anything I do to dad2 not affect dad1? It’s not the case apparently because when I add a son to dad2 it also adds the same son to dad1.

public struct Dad {
        public string name;
        public List <Son> sons;

        public struct Son {
            public string name;

            public Son (string n) {
                name = n;
            }
        }
    }

    static void Main (string [] args) {
        Dad dad1 = new Dad ();
        dad1.name = "Bob";
        dad1.sons = new List <Dad.Son> {new Dad.Son ("A")};

        Dad dad2 = dad1;
        Debug.WriteLine (dad2.Equals (dad1) + " " + dad1.sons.Count () + " " + dad2.sons.Count ());
        //true 1 1
        dad2.sons.Add ( new Dad.Son ("B"));
        Debug.WriteLine (dad2.Equals (dad1) + " " + dad1.sons.Count () + " " + dad2.sons.Count ());
        //true 2 2
    }

Answer 1

yes it makes a copy of the values inside the struct – and inside the struct there a reference to a List so that reference gets copied too – that is a “shallow copy”… if the List would have been copied over to a new object this would be a “deep copy”…
Struct assignment uses “copy” semantics which depends the copy semantics of each member… see http://msdn.microsoft.com/en-us/library/saxz13w4.aspx