Why does .net WCF Service require the Interface

Question

Unlike the asmx implementation the wcf requires for you to implement it's interface. I do not quite understand the reason behind that design. Interface is a contract between 2 classes...With that being said, how often do you have 2 wcf services that satisfry to the same interface but being implemented differently?

Another comment, the msdn strongly recommends to do this:

   MyService service = new MyService();

   try {

      service.DoWork();

   }
   catch(Exception) {}
   finally {
      service.Close();
   }

So let's say if I am to inject my service with using it's interface like this:

   public MyComponent : IDisposable
   {

       readonly IMyService service = null;

       public MyComponent(IMyService service) {

           this.service = service;

       }

       public DoWork() 
       {
           //some additional code.
           this.service.DoWork();

       }

       public void Dispose() 
       {
           //The Interface does not have the Close method,
           //So doing this defeats the whole purpose of polymorphysm
           (this.service as MyService).Close(); //Silly.
       }
   } 

How do you take the advantage of the interface with WCF?

Answer 1

No, WCF does NOT require you to have an interface and implement it.

It's just generally accepted best practice to do so - but you don't have to, if you don't want to.

If you want to, you can put your [ServiceContract] on a concrete class that has a number of [OperationContract] service methods - there's nothing stopping you from doing so.

But again: it's generally accepted and preached best practice to use an interface to separate out the actual contract as an interface (so you can e.g. mock it for testing etc.).

Answer 2

Actually, even MSDN concedes from time to time that the formality of interfaces may not always be "the right thing to do":

http://msdn.microsoft.com/en-us/library/ms733070.aspx

"The advantage of creating your services by applying ServiceContractAttribute and OperationContractAttribute directly to the class and the methods on the class, respectively, is speed and simplicity."