From: Dave Thomas <Dave@...>
Date: 2000-12-14T08:09:14+09:00
Subject: [ruby-talk:7178] Re: Multiple constructors.

"Conrad Schneiker" <schneik@us.ibm.com> writes:

> Someone asked me the following question. Is there some clever way to deal 
> with this?
> 
> # When creating a class, is "initialize" the only form of constructor?

The answer is yes and no.

Eventually, the only way to create an object is by calling
<classname>.new, which in turn calls <object>.initialize. So the
initialize method ends up doing the initialization of a constructed
object.

However, you can have any number of class methods that _act_ as
constructors, and which then invoke <classname>.new internally. In
fact, some classes even hide .new, so that you're forced to use these
alternative methods.

As a simple example (and one which is in very, very bad OO style, so
no flames please) you could have:

   class Rectangle
      def initialize(width, height)
        @width, @height = width, height
      end

      def Rectangle.square(side)
        Rectangle.new(side, side)
      end
   end

This would effectively give you two constructors

  r = Rectangle.new(2, 3)
  s = Rectangle.square(4)

Many of Ruby's built in classes to this (File.new vs. File.open, for
example).


Regards


Dave