From: Ian Hobson <NewGroups@...>
Date: 2003-12-23T17:51:55+09:00
Subject: Re: Copying methods from one class to another

In message <200312161434.02097.transami@runbox.com>, T. Onoma 
<transami@runbox.com> writes
>On Tuesday 16 December 2003 10:51 pm, Hacksaw wrote:
>>
>> No. Why would B and C be equal? B is a subclass of C. Specifically, methods
>> and variable defined in B are not reflected in C.
>>
>> The only way that they are equal is that an inherited method in B should do
>> the same thing as in C. Same with inherited variables.
>
>That's okay, I had the same difficulties understanding this at firs too. Let
>back up a bit. Look at this:
>
>   A = "1"
>   B = "2"
>   A = B
>
>What happens?
>
>  p A  # => "2"
>
>It's the same thing for classes. I know it's tempting to "over think" when
>classes are being delt with, I did the very same thing before I understood
>what was going on. But it really is that simple. After all, classes are
>objects just like strings.
>
>So lets do it again, but this time with less "syntatical sugar":
>
>  A = Class.new
>  B = Class.new(A)  # A is the superclass of B
>  A = B
>
>All that's happened is that A no longer points to its former self. Rather it
>now points to the same thing B does. The old A still exists as the superclass
>of B, but we no longer have a convienent constant to reference it by. Note
>that constants in Ruby are rather variable. The only thing that is noticably
>different is that Ruby spits out a warning saying we have redefined a
>constant.
>
>So, the short notation of
>
>  class A < A
>
>is the same as:
>
>  A = Class.new(A)
>
>and does the exact same thing as above, except that it dispenses with the go
>between constant B. And is analogous to doing this with a string:
>
>   str = " A new string " + str
>
This still does not answer the question of why? (At least for me), so 
I'm jumping in here are asking it again!

When you can simply extend class A with any new method you need, why do 
you want to create a subclass and pretend it is the class you started 
with?

Regards

Ian

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