From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-02-11T23:45:27+09:00
Subject: Re: inheriting from base classes

On Tue, Feb 11, 2003 at 11:40:14AM +0900, dblack@candle.superlink.net wrote:
> Hi --
> 
> Gavin Sinclair and I have been involved in an interesting exchange
> about the merits (or lack thereof) of inheriting from base classes, in
> particular String/Array/Hash.  This is also something that some of us
> were chatting about at the conference in November.
> 
> We're both very interested in hearing what people's views are on this.
> Do you ever subclass String, Array, and Hash?  Do you specifically
> avoid doing so?

I think Ruby貼s design favors aggregation over inheritance heavily. [I
understand matz does too :)]

There貼s a number of things against inheritance, in general:
 * you _have_ to know things about the implementation of superclasses
  since instance variables are not class-local
 * the probability of name clashes is too high if you add in modules and
  stuff 
 * delegation is so convenient in Ruby you tend to forget about
  inheritance, since subclassing is a very serious decision you cannot
  take lightly 
 * in general (although a little less pertinent to Ruby) designs based
  on object relationships (such as aggregation) are more flexible than
  those based on class relationships (more static, esp. in statically
  typed languages)

Moreover, the examples you gave really don貼t seem at all to satisfy the
貼is-a貼 rule of thumb. I貼d definitely go with aggregation there. 

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