From: Robert Klemme <shortcutter@...>
Date: 2006-09-21T00:20:13+09:00
Subject: Re: [ANN] Ducktator - A Duck Type Validator

On 20.09.2006 16:37, Ola Bini wrote:
> Austin Ziegler wrote:
>> On 9/19/06, Ola Bini <ola.bini@ki.se> wrote:
>>> Actually, the name is more about the fact that you can use regular
>>> duck-type techniques (like respond_to?),
>>
>> Note: if you're calling #respond_to? you're not doing duck typing.
>> You're doing contract validation, perhaps, but not duck typing. Duck
>> typing is just calling a method and expecting that it will be
>> implemented. It's *trusting* your callers to do the right thing.
>>
>> Now, I sometimes use #respond_to? -- but it isn't duck typing.
> 
> I beg to differ, and according to the pick-axe, this interpretation is 
> correct. Duck-typing isn't to *trust* your callers. Duck typing is to 
> check if something quacks like a duck and walks like a duck. 

Definitively not.  What do you do if that method returns false? 
Basically you can only raise an exception.  Of course, you can use a 
different exception type and message but that's it.

If you need respond_to? to choose a different path of execution because 
a method needs to cope with different types that's ok but it's not duck 
typing.

Regards

	robert