IsAssignableFrom, IsInstanceOfType and the is keyword, what is the difference?

Question

I have an extension method to safe casting objects, that looks like this:

public static T SafeCastAs(this object obj) {
    if (obj == null)
                


        

Answer 1

These functions and operators have different meaning. If you have objects you can always get types. so you do not work on what you have, but you do what needs to be done.

When you are working with a class hierarchy differences are very clear.

Look at following example

      class ABase
        {

        }

        class BSubclass : ABase
        {

        }
    ABase aBaseObj = new ABase();
                BSubclass bSubclassObj = new BSubclass();

                ABase subObjInBaseRef = new BSubclass();

Different operations yield different results.

typeof(ABase).IsInstanceOfType(aBaseObj) = True

typeof(ABase).IsInstanceOfType(bSubclassObj) = True

typeof(ABase).IsInstanceOfType(bSubclassObj) = True

typeof(BSubclass).IsInstanceOfType(aBaseObj) = False

bSubclassObj is ABase = True

aBaseObj is BSubclass = False

subObjInBaseRef is BSubclass = True

subObjInBaseRef is BSubclass = True

typeof(ABase).IsAssignableFrom(typeof(BSubclass))  = True

typeof(BSubclass).IsAssignableFrom(typeof(ABase))= False

In case on no hierarchy, may be everything was same. But if you work with hierarchy, IsAssignableFrom , is , and IsInstanceOfType yield different results.

There are more possible combinations that could be tried. For example, you can introduce a class C which is not related in anyway with existing classes in this example.