From: Tim Hunter <Tim.Hunter@...>
Date: 2003-02-11T23:18:40+09:00
Subject: Re: inheriting from base classes

The ImageList class in RMagick is a subclass of Array. An ImageList is
an array of images, plus an index value that addresses the "current"
image.

Yes, there's a "looseness of fit."  There's a handful of methods that
just don't apply to an array of images: to_s, pack, etc. Since by
definition an ImageList can only contain images, assoc, flatten, and
such-like also don't apply.  These methods are undefined in ImageList.

There's a method in ImageList for every Array method. Array methods
that return Arrays (+, for example) call "self.class.new.replace" to
convert the Arrays that the super returns into ImageLists. (Yes,
ImageList#replace gets a lot of work.)

Adding an Array to an ImageList works, as long as the array contains
only images, and yields an ImageList. Adding an ImageList to an Array
yields an Array, which is what I think you'd expect.

My first cut at ImageList had ImageList _contain_ an array of images
and the usual accessor methods for the array, but this was just too
clunky. For example,

	mylist.images << newimage

is clunky compared to

	mylist << newimage


On Tue, 11 Feb 2003 11:40:14 +0900, dblack@candle.superlink.net wrote:
>
>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?
>