When is obj.GetType().IsInstanceOfType(typeof(MyClass)) true?

Question

I\'m looking at this piece of code written by someone else, and I\'m wondering when it would evaluate to true. Basically, it is saying someType is an instance of someOtherT

Answer 1

The Type.IsInstanceOf documentation says that Type.IsInstanceOfType(o) return "true if the current Type is in the inheritance hierarchy of the object represented by o, or if the current Type is an interface that o supports."

In the above examples, the Type is the type returned by GetType(), so it is the type of the object at the far left. The object o is typeof(BaseClass), which is of type Type. The current Type is DerivedClass and the object o is typeof(BaseClass). The type of o is Type.

Plug that into the documentation. It returns "true if DerivedClass is in the inheritance hierarchy of Type."

This is rarely true.

The author almost certainly intended typeof(BaseClass).IsInstanceOfType(derivedClass), which is much more easily written as derivedClass is BaseClass.