From: Rick DeNatale <rick.denatale@...>
Date: 2007-03-20T23:25:21+09:00
Subject: Re: does Ruby not support multiple "initialize" methods for a class???

On 3/20/07, Emilio Tagua <miloops@gmail.com> wrote:

> You could use:
>
> class Invitation
>   attr_reader :id, :date, :user, :text, :email
>
>   def Invitation.withId(id)
>     return self.new(id)
>   end
>
>   def Invitation.withAll(id, date, user, email, text)
>       return self.new(id, date, user, email, text)
>   end
>
>   def initialize(id = 0, date = '', user = '', email = '', text = '')
>     super()
>     @id = id
>     @date = date
>     @email = email
>     @user = user
>     @text = text
>   end
> end
>
> then:
>
> invitation = Invitation.withId(1)
>
> or with all params.

Of course the only thing that the withId and withAll (*which in more
normal Ruby style should be with_id and with _all) do is throw an
error if you don't call them with the right number of parameters.

With the above code you can also write:

  Invitation.new
Invitation.new(42)
Invitation.new(99, '10/22/2006')
Invitation.new(35, '3/2/1907', 'Teddy Roosevelt')
Invitation.new(67, '10/12/2010', 'Arthur C. Clarke', 'TheMan@theFuture.org')
or
Invitation.new(88, '6/6/1945', 'Dwight Eisenhower', 'leader@us.mil',
'I like Ike')

Any of these work as defaults are provide dor all.

Another approach would be to use a Hash to provide 'keyword' arguments.

Invitation.new(:id => 20, :email => 'somene@somewhere.com')

The initialize method would need to pick the hash argument apart.

    def initialize(options={})
         # process options and set iv's etc.
    end

You could combine this with additional parameters before the hash parameter.

* Normal ruby style is to reserve 'camel case' for Globals (e.g. class
and module names) and use underscores as separators in variable names.
 I keep tripping up on that when my old Smalltalk habits kick in.
It's not crucial, but when in Ruby do as the Rubyists do.
-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/