From: Franz GEIGER <fgeiger@...>
Date: 2001-01-03T04:40:02+09:00
Subject: [ruby-talk:8534] Re: design question

What about private inheritance in this situation? Wouldn't it save a lot of
work AND enable me to hide the methods I don't like to expose to the public?

Regards
Franz GEIGER

"Kevin Smith" <sent@qualitycode.com> wrote in message
news:0G6H0012WVQMJY@mta5.snfc21.pbi.net...
> chad fowler wrote:
> >In the Java world, I tend to encapsulate Java's
> >supplied libraries/types by composing things like
> >collections inside my own domain objects.  So, for
> >example, to create a collection ("People") or "Person"
> >objects, I would create a "People" class with a
> >limited interface that delegated any requests for
> >members of the list to an internal representation
> >which I could vary at a later time (like an ArrayList
> >or something like that).
> >
> >The problems I'm trying to solve by doing that in Java
> >are: 1) I don't want to expose an explicit type which
> >is not under my control as part of an externally
> >visible interface, 2) I want to be able to vary the
> >internal representation at any time, 3) I want to take
> >care of type casting--mine is a colleciton of
> >"Person"s, not "Object"s 4) I want my intent to be as
> >clear as possible (users of my classes won't have to
> >think "What is this array for?").
> >
> >So, my question is:  What are the recommended
> >practices in Ruby?  Do folks generally inherit the
> >supplied Ruby classes or do they try to use delegation
> >in the same way I've outlined above?  It seems that a
> >lot of my reasons for using composition/delegation are
> >somewhat irrelevant in Ruby, but it still feels really
> >weird to extend an Array to create a domain-specific
> >list.
>
> I've only been working in Ruby for a couple
> months, and my background is in C++ rather than
> Java. But I think I understand your question.
> Basically, you're asking whether in Ruby you
> would tend to have People inherit from Array or
> contain an Array member.
>
> In my mind, the issue is whether you want to
> expose *all* of the Array members as the
> interface, or to create your own limited or
> different interface. Do you want client code to
> be able to sort your people at any time, for
> example. Are you concerned that client code might
> stuff a car into your list of people?
>
> If you want control over the interface, then you
> would want to contain (aka delegate)*, not
> inherit. That's as true in Ruby as it is in Java
> or C++. Thus, I would tend to delegate when
> creating a specific class like People, but would
> inherit when creating a generic improvement on a
> built-in class, like "StreamableHash".
>
> * = Note that my use of the word "delegate" here
> is not related to the 'delegate' module that
> ships with Ruby.
>
> Kevin