Base Class = New Derived Class. How does this work?

Question

Say I have a base class called Enemy and a derived class called Ogre.

What is the difference between creating an instance these two ways:

Enemy newOgre = new Ogre();

Ogre newOgre = new Ogre();

Answer 1

Actually, the piece of code that is creating the instance is only new Ogre(). What is in the left side of the equal sign has nothing to do with creating the instance.

The first statement is simply assigning the created instance to a variable of type Enemy. The second one is assigning it to a variable of type Ogre.

So you have two variables of different types pointing to objects of the same type, i.e. Ogre.

The variable (what is on the left side of the equal sign), only determines what you can access from the object. For example, if the Ogre class has a method that is not inherited from Enemy, then using the Enemy variable, you will not be able to access it.

Please note that the variable does not effect how the object behave. For example, if Ogre overrides a method defined in Enemy that does something different. Calling this method on an instance of Ogre using a variable of type Enemy would cause the overridden method in Ogre to be invoked, not the one in Enemy,

For example, consider these classes:

public class Enemy
{
    public virtual void Test()
    {
        Console.WriteLine("enemy");
    }
}

public class Ogre: Enemy
{
    public override void Test()
    {
        Console.WriteLine("ogre");
    }
}

Now if you do this:

Orge enemy = new Orge();
enemy.Test();

The console would print "ogre".

And if you do this:

Enemy enemy = new Ogre();
enemy.Test();

The console would still print "orge".