Polymorphism in VB.NET

Question

In VB.NET, say I have a function

Public Function Foo(ByVal currentShape as Shape)

Instead up passing in a Shape object, I pass in a subclass of Shape called Square like such:

Dim square As Square = new Square()
Foo(square)

Do I need to convert my Square object to a Shape object before passing it in? If so, how do I do this?

Answer 1

Square is-a Shape .
You don't need to convert anything.

All subclasses are implicitly convertible to their superclasses.

Answer 2

No, you don't need to perform a conversion yourself. The value of square can be converted using a reference conversion to a value of type Shape (it's still a reference). This does not create a new object - it just looks at the object in a different way :) Foo will only be able to access members declared in Shape , although they may be overridden in Square .

Any changes made to the object within Foo will still be visible via square when the method returns.

Answer 3

我很确定您可以直接传递Square对象。