Initialize base class in .NET

Question

How do I go about if I need to initialize an object's base with existing object? For example, in this scenario:

public class A
{
    public string field1;
    public string field2;
}

public class B : A
{
    public string field3;
    public void Assign(A source)
    {
        this.base = source; // <-- will not work, what can I do here?
    }
}

Assign() method can, obviously assign values to the base class field-by-field, but isn't there a better solution? Since class B inherits from A, there must be a way to just assign A to the B.base

In C++ this would be a trivial thing to do, but I can't seem to grasp how to do this in .NET

Answer 1

Unfortunately base is readonly.

[Edit]
Well perhaps not so unfortunate. The relationship between a base class and a child class is IS-A not HAS-A. By allowing a child class to change the instance of the base class you are allowing the child class to change its own reference since it IS-A base class. If you truly need this functionality then I would suggest you change your inheritance model to reflect what you truly want to do.

Something like this:

public class A
{
    public string field1;
    public string field2;
}

public class B
{
    public string field3;
    public A a;

    public void Assign(A source)
    {
        this.a = source;
    }
}

seems more appropriate and has clearer meaning and functionality.

Answer 2

        public Assign(A a)
        {
            foreach (var prop in typeof(A).GetProperties())
            {
                this.GetType().GetProperty(prop.Name).SetValue(this, prop.GetValue(a, null),null);
            }
        }

Basically, it uses reflection to get all the properties of the base and assign the values of this, to all the values that exist in A.

EDIT: To all you naysayers out there, I quickly tested this now with a base class that had 100 integer variables. I then had this assign method in a subclass. It took 46 milliseconds to run. I don't know about you, but I'm totally fine with that.