From: Dave Thomas <Dave@...>
Date: 2001-05-08T21:44:28+09:00
Subject: [ruby-talk:14862] Re: Polymorphic methods

"Benjamin J. Tilly" <ben_tilly@operamail.com> writes:

> >> m = Month.new(12)
> >> m = Month.new('December')
> >> m = Month.new(anotherMonth)
> >
> >I'd like to know how to do that in ruby too, but my impression is
> >that you just have to test the type.

> But there is no way to remove the fact that if the type is to matter
> then it must be tested, and logic that exists must be written.

Ben:

I think that might be a little absolute :)  Wasn't it you who posted
the double-dispatch example a couple of days ago? We could code the
above without a condition in sight (apart from validation).

   class Integer
     def to_month
       if self >= 1 and self <= 12
          self
       else
          raise "bad month"
       end
     end
   end

   class String
     def to_month
       { 'January' => 1, 'February' => 2, ...}[self] || raise "bad month"
     end
   end


   class Month
     def initialize(from)
       @month_number = from.to_month
     end

     def to_month
       @month_number
     end
   end


Dave