From: Dave Thomas <dave@...>
Date: 2003-06-12T14:29:49+09:00
Subject: Re: Multiple Initialize methods?

Nick wrote:
> Hi everybody,
> 
> Thanks for the replies.  I appreciate Ruby isnt C++, or C# or Delphi, or ...
> but typically you can have more than one constructor in those languages -
> because typically people have requested the functionality from the language
> because they help.  I think I will reluctantly go with the setting default
> values for the params.  Its not nice in my view, but it will do.

I haven't followed this thread, but has anyone suggested construction 
methods (sometimes called factory methods?). Make the constructor 
private, and use class methods to construct specific objects:


   class Square
      def Square.with_area(area)
	new(Math.sqrt(area))
      end

      def Square.with_diagonal(diag)
          new(diag/Math.sqrt(2))
      end

      def Square.with_side(side)
          new(side)
      end

      private_class_method :new

      def initialize(side)
        @side = side
      end

   end

   s1 = Square.with_area(4)
   s2 = Square.with_diagonal(2.828427)
   s3 = Square.with_side(2)


The joy of this approach is that not everything has to be done in the 
constructor: because no one else can call it, the constructor can create 
a partially initialized object, leaving it up to your construction 
methods to complete the job.


Cheers



Dave