From: Phrogz <phrogz@...>
Date: 2007-11-01T12:20:01+09:00
Subject: Re: why, or when to, use a class method?

On Oct 31, 5:28 pm, Thufir <hawat.thu...@gmail.com> wrote:
> On Oct 31, 2:17 pm, 7stud -- <bbxx789_0...@yahoo.com> wrote:
> What would be a case where there's a SongList object, though?  Or, if
> there are class methods then generally there won't be objects of that
> class?

  class Rectangle
    def self.all
      @all ||= []
    end

    def initialize( width, length )
      @width, @length = width, length
      self.class.all << self
    end

    def self.square( length )
      new( length, length
    end

    def self.double( width )
      new( width, width * 2 )
    end
  end

  r1 = Rectangle.new( 5, 7 )
  r2 = Rectangle.square( 15 )
  r3 = Rectangle.double( 6 )
  p Rectangle.all

That's a very simple example of two common situations for me: using
class methods to report information about all instances of the class
(which I'm manually tracking here), and using class methods as
alternative constructors that return specialized instances.