From: Chad Fowler <chadfowler@...>
Date: 2003-02-12T01:48:09+09:00
Subject: Re: inheriting from base classes

Michael Campbell wrote:

>>But a further question is: how fundamental is the inheritance
>>hierarchy
>>to designing programs in Ruby, given the non-kind_of? underpinnings
>>of
>>Ruby objects (i.e., their dynanism and "in-the-moment" behavior)?
>>    
>>
>
>
>Are you saying here that because it's easy to not do strict kind-of?
>modelling in ruby, that you shouldn't?  Or that existing classes in
>ruby don't do it, so end users shouldn't have to?  Or something else?
>
>Your previous post seemed to indicate you break the kind-of? "rule of
>thumb" where it becomes convenient to save typing, which I think is
>not the way it should be done.  not that I've never done the same
>thing, but we're at a more conceptual level with this discussion. 
>(Or are we?  maybe that's a disconnect.)
>
>
>  
>
I wouldn't say this is an issue of saving typing (as in pushing keys on 
a keyboard).  My guess is that David feels that this is the "Ruby spirit".

I'm a static->dynamic language convert (not that I'm going to preach 
about either), and while I understand all of the is-a/has-a stuff and 
have practiced it for years, I find that in Ruby I stop worrying about 
type so much.  I give myself a lot more flexibility to be expressive and 
succinct.  Maybe I'll add a method to an existing class.  Maybe to an 
instance.  In languages like Java, I tend to *never* use the equivalent 
of  Ruby's Array in public interfaces, because I'm so driven by the Java 
strict typing Way. 

So, I see where David's coming from here.  There are rules of thumb on 
OO design, but the Ruby environment places higher value on 
"responds-to?" than "is-a?" ...at least in my interpretation of it.

That having been said, these days I find myself (in Ruby, at least) 
almost never inheriting from anything.  Again, I'm not dogmatically 
saying that you *shouldn't* use inheritance.  I just tend to do what a) 
feels right, b) gets the job done, and c) others can read (if that's 
even necessary).

Chad