Cast type to IDisposable - Why?

Question

Saw this. Why the explicit cast to IDisposable? Is this just a shorthand to ensure that IDisposable is called on exiting the using block?

using (proxy as IDi         


        

Answer 1

It's unnecessary as the using statement is explicitly tied to the IDisposable interface, per the MSDN docs

Provides a convenient syntax that ensures the correct use of IDisposable objects.

edit: The C# language spec (sec. 8.13) provides three possible expansions for the using statement's syntactic sugar:

A using statement of the form

using (ResourceType resource = expression) statement

corresponds to one of three possible expansions. When ResourceType is a non-nullable value type, the expansion is

{
   ResourceType resource = expression;
   try {
      statement;
   }
   finally {
      ((IDisposable)resource).Dispose();
   }
}

Otherwise, when ResourceType is a nullable value type or a reference type other than dynamic, the expansion is

{
   ResourceType resource = expression;
   try {
      statement;
   }
   finally {
      if (resource != null) ((IDisposable)resource).Dispose();
   }
}

Otherwise, when ResourceType is dynamic, the expansion is

{
   ResourceType resource = expression;
   IDisposable d = (IDisposable)resource;
   try {
      statement;
   }
   finally {
      if (d != null) d.Dispose();
   }
}

Note that in each one of these expansions the cast is done anyway, so as originally stated, the as IDisposable is unnecessary.