c# - Casting between two types derived from the (same) interface

Question

I have an interface and two types that derive from it.

However, I cannot do the following:

B objectB = (B) objectA

Where B derives from Interface1 (I am making up the name of classes but the point still stands), and likewise for objectA (which is of type A). I get the following error message:

Cannot cast expression of type A to B.

Both types are deriving from the interface, what am I missing?

Answer 1

1. Types do not derive from an interface. They implement an interface.
2. The fact that both an Elephant and a Spider are Animals doesn't mean that you can convert one to the other.