From: Josh Cheek <josh.cheek@...>
Date: 2011-10-11T12:27:51+09:00
Subject: Re: Basic OO Class question

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On Mon, Oct 10, 2011 at 3:55 AM, Robert Klemme
<shortcutter@googlemail.com>wrote:

> On Mon, Oct 10, 2011 at 2:53 AM, Josh Cheek <josh.cheek@gmail.com> wrote:
> > On Sun, Oct 9, 2011 at 5:44 PM, Kevin E. <kellwood@gmail.com> wrote:
> >
> >> Hi All
> >>
> >> I am try to get up to speed on several things at once; namely, OO and
> >> also Ruby.  I have written a bunch or Ruby scripts to perform various
> >> text processing tasks but I think I want to start learning something
> >> about OO Programming.  I do have the book "Programming Ruby" and it is a
> >> great help.
> >>
> >> My question is related to writing a class for something like a polygon.
> >> It can be described by a few integer and string properties. So I could
> >> do something like this snippet:
> >>
> >> class Zone
> >>
> >>    attr_accessor :type, :length
> >>
> >>    def initialize(type, length)
> >>      @type = type
> >>      @length = length
> >>    end
> >>
> >> end
> >>
> >> testZ = Zone.new("Rad", 20.1)
> >>
> >> Here is what I don't know how to do.  How do I add an array of integers
> >> to this class?  It would need to be of variable length.
>
> > Give it an accessor and then initialize the associated instance variable
> to
> > an array.
> >
> >
> > class Zone
> >
> >  attr_accessor :type, :length, :integers
> >
> >  def initialize(type, length)
> >    @type = type
> >    @length = length
> >    @integers = Array.new
> >  end
> >
> > end
> >
> > test_z = Zone.new("Rad", 20.1)
> > test_z.integers # => []
> > test_z.integers << 1
> > test_z.integers # => [1]
> > test_z.integers << 2
> > test_z.integers # => [1, 2]
> >
> >
> > In terms of the integers part, you can't specify the array should contain
> > integers, I've named it integers to indicate that's what it is, but
> really
> > you could put anything in there.
>
> That's one of the reasons why I sometimes prefer a more robust approach
>
> class Zone
>
>  attr_accessor :type, :length
>
>  def initialize(type, length)
>   @type = type
>   @length = length
>    @integers = [] # same as Array.new
>  end
>
>  def add(an_int)
>    @integers << an_int.to_int
>    self
>  end
>
>  def integers
>    @integers.dup
>  end
> end
>
> This does two things:
>
> 1. ensure that only integers are put into the array by doing conversion
> #to_int.
>
> 2. copies the array on access to avoid someone outside the instance to
> mess with internal state.
>
> Whether this added robustness is needed depends on the application.
> You like also have to add methods for removing entries again etc.
>
>
Interesting, I like it. I usually only dup data if I find I need it, but for
lib code it probably makes sense to be more proactive. I'm a bit ambivalent
about to_int, though, I suppose it depends on the situation.

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