Question

Recently I’ve run into strange issue related to casting. Every discussion/post I’ve seen tends to revolve around using casting when one is sure about the object being casted plus a couple of details. I haven’t however found what’s the reasoning behind the code below:

class Program
{
    static void Main(string[] args)
    {
        var h = new SomeCommandHandler();
        var c = h as ICommandHandler<ICommand>; //this works as expected
        //var c = (ICommandHandler<ICommand>)h; //this throws - why?
    }

    interface ICommand { }
    class SomeCommand : ICommand { }

    interface ICommandHandler<I> where I : ICommand { }
    class SomeCommandHandler : ICommandHandler<SomeCommand> { }
}

So why the second call throws an exception? What’s the difference between casting and as operator that I’m not aware of?

EDIT:
It wpuld throw in the commented line above
“Unhandled Exception: System.InvalidCastException: Unable to cast object of type ‘SomeCommandHandler’ to type ‘ICommandHandler`1[ConsoleApplication1.Program+ICommand]'”

Answer 1

Well, that’s the whole entire difference right there. The as operator returns null if the object can’t be cast to that type, and just casting produces an exception.