why an object of WCF service contract interface can be casted to IClientChannel

Question

In WCF Client Architecture, it says

When using the ChannelFactory class with a service contract interface, you must cast to the IClientChannel interface t

Answer 1

I was recently was studying the same thing, because I was trying to figure out why I could cast my channel as an ICommunicationObject as I saw some of the WCF source code doing.

basically .NET has the type information it needs at runtime.

let's say we have a class that implements an interface

class Foo: IFoo {}

you can declare the object like this

IFoo instance = new Foo()

but you can also cast the instance directly as a Foo()

Foo cast = (Foo)instance;

Because an object can be cast or converted to its type at runtime.

---

So what is WCF doing?

For fun, try to instantiate a channel factory with your own interface

IFoo instance = new ChannelFactory<IFoo>()

you'll get a runtime exception.

"InvalidOperationException Attempted to get contract type for IFoo, but that type is not a ServiceContract, nor does it
inherit a ServiceContract."

When you decorate an interface with the [ServiceContract] attribute, the WCF runtime picks this up and builds all the classes that WCF needs to build your channel.

This includes interfaces like ICommunicationObject, IChannelFactory<TChannel>, IClientChannel, etc.

So although the factory method exposes your instance as an IFoo, at runtime it also has the other interfaces WCF needs to run.

---

Finally, the reason that channel.GetType() returns an ICalculatory, is because GetType() is returning the runtime type of that object. By casting to an IClientChannel, you are performing a type conversion that WCF guarantees will succeed.