This really, really urks me, so I hope that someone can give me a reasonable justification for why things are as they are.
NotImplementedException. You are pulling my leg, right?
No, I'm not going to take the cheap stab at this by saying, "hang on, the method is implemented – it throws a NotImplementedException." Yes, that's right, you have to implement the method to throw a NotImplementedException (unlike a pure virtual function call in C++ – now that makes sense!). While that's pretty damn funny, there is a more serious problem in my mind.
I just wonder, in the presence of the NotImplementedException, how can anyone do anything with .Net? Are you expected to wrap every abstract method call with a try catch block to guard against methods that might not be implemented? If you catch such an exception, what the heck are you supposed to do with it??
I see no way to test if a method is actually implemented without calling it. Since calling it may have side effects, I can't do all my checks up-front and then run my algorithm. I have to run my algorithm, catch NotImplementedExceptions and the some how roll back my application to some sane state.
It's crazy. Mad. Insane. So the question is: Why does the NotImplementedException exist?
As a preemptive strike, I do not want anyone to respond with, "because designers need to put this in the auto-generated code." This is horrid. I would rather the auto-generated code not compile until you supply an implementation. For example, the auto generated implementation could be "throw NotImplementedException;" where the NotImplementedException is not defined!
Has anyone ever caught and handled a NotImplementedException? Have you ever left a NotImplementedException in your code? If so, did this represent a time bomb (ie, you accidentally left it there), or a design flaw (the method should not be implemented and will never be called)?
I'm very suspicious of the NotSupportedException also… Not supported? What the? If it's not supported, why is it part of your interface? Can anyone at Microsoft spell improper inheritance? But I might start another question for that if I don't get too abuse for this one.
This is an interesting read on the subject.
There seems to be a strong agreement with Brad Abrams that "NotImplementedException is for functionality that is just not yet implemented, but really should (and will be). Something like what you might start with when you are building a class, get all the methods there throwing NotImplementedException, then flush them out with real code…"
Comments from Jared Parsons are very weak and should probably be ignored: NotImplementedException: Throw this exception when a type does not implement a method for any other reason.
The MSDN is even weaker on the subject, merely stating that, "The exception that is thrown when a requested method or operation is not implemented."