From: firstname@... (Hans Fugal)
Date: 2003-12-16T00:07:08+09:00
Subject: Subclassing Array

I have a simple observer-like module:
module Notifier
    def add_notification(&callback)
	@notifications = [] if not defined? @notifications
	@notifications << callback
    end

    def delete_notification( &callback )
	@notifications.delete(callback) if @notifications
    end

protected
    def notify
	@notifications.each { |o| o.call } if defined? @notifications
    end
end

(If 'Notifier' bugs you, then do a semantic search and replace
/notify/observe/)

I want to mix this in to a subclass of Array. The resulting class would
behave exactly like an Array except whenever the array changed notify
would be called.

I *could* subclass Array and def each of
     &, *, +, --, <<, <=>, ==, ===, [], [], []=, assoc, at, clear,
     collect, collect!, compact, compact!, concat, delete, delete_at,
     delete_if, each, each_index, empty?, eql?, fill, first, flatten,
     flatten!, include?, index, indexes, indices, join, last, length,
     map!, new, nitems, pack, pop, push, rassoc, reject!, replace,
     reverse, reverse!, reverse_each, rindex, shift, size, slice,
     slice!, sort, sort!, to_a, to_ary, to_s, uniq, uniq!, unshift, |
that changes the Array, but obviously this isn't an exciting prospect.
I'm hoping that most of the changing methods of Array are actually
implemented in terms of a couple of fundamental methods, e.g. insert and
delete. So I would do:

class NotifyingArray
    include Notifier
    def insert(o)
	super(o)
	notify
    end
    def delete(o)
	super(o)
	notify
    end
end

Am I on the right track? Does anyone know which methods I would have to
override?

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