From: Hal Fulton <hal9000@...>
Date: 2005-05-09T23:42:44+09:00
Subject: An idiom I like... modifiable defaults

Just thought I'd share a little concept that I find
useful. Your comments are welcome.

Sometimes objects are created with certain defaults.
One way to override them is with default values in
the constructor (and often corresponding writer methods).

But sometimes I "don't like" the default and want to
change it (for this program/session).

Often I use class-level accessors for that purpose.

Here's a contrived example...


Cheers,
Hal


   class Text

     class << self
       attr_accessor :color
       Text.color = "black"
     end

     attr_accessor :color

     def initialize(txt, color="black")
   # Hint: You can improve this further by saying
   # def initialize(txt, color=Text.color)
       puts "#{color} text..."
     end
   end


   # The old way...

   a = Text.new("some")           # black
   b = Text.new("random","blue")  # blue
   c = Text.new("text")           # black
   c.color = "blue"               # but now it's blue

   # The new way...

   Text.color = "blue"

   e = Text.new("Ruby is cool")   # blue
   f = Text.new("as dry ice")     # blue