From: Joe Cheng <code@...>
Date: 2003-08-29T22:18:26+09:00
Subject: Re: Ruby OO-newbie design-question

Hi Per,

Unless a, b, and c have different behavior (not just values), I think you
can do it with a single class:

class Node
    include Enumerable

    def initialize
        @parent = nil
        @children = []
        @values = {}
    end

    def each(&b)
        @children.each &b
    end

    def add_child(child)
        child.parent = self
        @children << child
    end

    def remove_child(child)
        child.parent = nil
        @children.delete(child)
    end

    def [](key)
        # if the value exists locally, return it; otherwise, if parent
exists, ask it
        @values[key] or (@parent and @parent[key])
    end

    def []=(key, value)
        @values[key] = value
    end

    protected

    def parent=(parent)
        @parent = parent
    end
end

# Then you can do this:
a1 = Node.new
b1 = Node.new
a1.add_child(b1)
c1 = Node.new
b1.add_child(c1)
b2 = Node.new
a1.add_child(b2)
# and so on...

a1['color'] = 'purple'
b1['color'] = 'yellow'
puts b2['color']  # 'purple'
puts c1['color']  # 'yellow'
puts c1['nothing']  # nil

Is that what you had in mind?

"Per Wigren" <wigren@home.se> wrote in message news:3f4f3875_2@127.0.0.1...
> Hi!
> I'm not at all new to programming, I know OO-concepts but I don't have any
> hands-on experience with designing/programming OO except for small tests.
> I'm also a Ruby newbie, but have been coding a LOT of C, (advanced)
> Shellscripts and Python.
>
> I need advice on good design, taking features of Ruby into consideration.
>
> I want a tree of objects like this:
>
> a1
>  b1
>   c1
>  b2
>   c1
>   c2
>    d1
>
> and so on...  The a#-objects will hold default values and methods for b#
and
> b# will hold default values for c# and so on. When a value in a# is
changed
> I want its children to immediatly inherit them also, if they aren't
> overridden. b# will be subclasses of a#, c# will be subclasses of b# etc.
> I have to be able to dynamically (at runtime) add and delete children.
>
> What is a good way to design this with the OO-features of Ruby, keeping it
> as readable and clean as possible?
>
> Regards,
> Per Wigren
>