duck-type-checking?

[paul]

Ben Finney schrieb:
> Joe Strout <joe at strout.net> writes:
>> "x quacks like a basestring if it implements all the public methods
>> of basestring, and can be used in pretty much any context that a
>> basestring can."
> 
> That is not duck typing. Rather than checking what foo does in
> response to prodding that, by your admission, is only designed to find
> out what type it is, duck typing instead advocates that you should use
> foo *as though it is known to be* the type of object you want. If it
> is not suitable, then appropriate exceptions will be raised and either
> caught by some code that knows how to handle them, or crash the
> program.

Warning, rant ;)

This whole theory breaks down quickly if you're writing library code. 
How do your unittests help the user of your library to use it correctly? 
How do you communicate incorrect usage of your interfaces to the user?

If you are able to specify the type of the arguments as part of the 
interface the compiler/interpreter will help you. Types are used to 
describe behaviour (if thats a good thing, I don't know). While python 
has strong types, there could be used better (instead it gets worse, see 
the suddently-not-sortable-list-type diskussion and the endless 
repetition of the greatest of all after-the-fact theories ever "duck 
typing".

cheers
  Paul

BTW: Back to Java? No, not really.