From: David Alan Black <dblack@...>
Date: 2002-05-04T12:26:24+09:00
Subject: Re: ruby idiom check

Hello --

On Sat, 4 May 2002, Mark Probert wrote:

>
> I have a class that telnets into a number of different
> systems.  Each of these systems has it own set of defaults
> such as ports, address, username, and so on.
>
> The thought I had to abstract this was (1) to sub-class
> or (2) to use Struct to contain the differences, a la:
>
>
> SysDefs  = Struct::new(:name, :val)
>
> $OneDef = SysDefs::new('type 1', 123)
> $TwoDef = SysDefs::new('type 2', 234)
>
> class BasicSys
>      attr_reader :name, :val, :stuff
>
>      def initialize(key=1)
>          @def = SysDefs::new
>          case key
>          when 1
>              @def = $OneDef
>          when 2
>              @def = $TwoDef
>          end
>          @name = @def.name
>          @val  = @def.val
>          @stuff = nil
>      end
> end
>
> Any thoughts as to which is the preferred design choice
> and why?

I would tend to want to get rid of the global variables, and also to
confine the knowledge of the hash keys to as small a space as
possible.

Here's an example of this (probably not optimal, but anyway).  The
SysDefs module contains one method which knows about the names of the
keys, and one method which returns a hash based on a key.  I've also
done some other things differently, just for fun -- for example,
instead of assigning :name and :val values to @name and @value, I've
just made BasicSys inherit from Hash.  (This may or may not make sense
for your actual application.)

  module SysDefs
    def defs
      default = ["type 1", 123]
      defs = [
        default,
        ["type 2", 234]
      ]
    end

    def get_def(key)
      spec = defs.detect{ |d| /#{key}/.match(d[0]) }
      Hash[:name => spec[0], :val => spec[1]]
    end

  end

  class BasicSys < Hash
    include SysDefs

    def initialize(*key)
      replace get_def(key)
    end
  end

# Mini-test:
  p BasicSys.new    # =>  {:val=>123, :name=>"type 1"}
  p BasicSys.new(2) # =>  {:val=>234, :name=>"type 2"}

David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav