Question

If I have a class like this:

class A {
    public string fe = "A";
}

And a class that inherits from it like so:

class B : A {
    public string fe = "B";
}

Visual C# will tell me that B.fe hides A.fe so I should use the new keyword. So I change class B to look like:

class B : A {
    public new string fe = "B";
}

And then I have a function that takes an A (but, by virtue of inheritance, will also take a B) like this:

class D {
    public static void blah(A anAObject) {
        Console.Writeline(A.fe);
    }
}

Even when I pass it an instance of a B object, which it will take without question, it will print “A”! Why is this, and how can I make it work how I want without setting the variable in the constructor?

Answer 1

That’s the difference between override and new. new defines a member which happens to have the same name as a member in the base class. It doesn’t override that member. So if you have a method that expects an A instance, it will take the value of A.fe and not the member in the derived class with the same name.

Use a property with override instead:

class A {
    public virtual string fe { get { return "A"; } }
}

class B : A {
    public override string fe { get { return "B"; } }
}