From: Rick DeNatale <rick.denatale@...>
Date: 2008-02-13T06:41:52+09:00
Subject: Re: Subclassing Integer; solved!

On 2/12/08, ThoML <micathom@gmail.com> wrote:
> > > Year.new(2008).class # => Fixnum
> > > Year.new(2008) == 2008 # => true
> >
> > That's exactly what I want.
>
> The latter gives false with ruby19 though. Also it seems impossible to
> define a method in Year.
>
>     class Year < Integer
>         def foo
>             self * 2000
>         end
>     end
>     Year.new(2008).foo
>     # NoMethodError: undefined method `foo' for 2008:Fixnum
>
> Also, I don't quite understand the hack with inherited() since it
> doesn't do anything. The reason why the class() method returns
> 'Fixnum' is not because of the inheritance but because of
> #method_missing.

Well you really can define a method in Year, it's just that Year.new
doesn't return an instance of Year, it returns an instance of
BoxedInteger (not Fixnum as I had said earlier.)

> A IMHO slightly more accessible/"traditional" way to
> achieve the same would be:
>
>     class Year < BasicObject
>         def initialize(value)
>             @value = value
>         end
>
>         def foo
>             @value * 2000
>         end
>
>         def ==(other)
>             @value == other
>         end
>
>         def respond_to?
>             @value.respond_to?
>         end
>
>         private
>         def method_missing(meth, *args, &block)
>             @value.send meth, *args, &block
>         end
>     end
>
>     Year.new(2008).class
>     # => Fixnum
>     Year.new(2008).foo
>     # => 4016000
>     Year.new(2008) == 2008
>     # => true
>     Year.new(2008).class.superclass
>     # => Integer
>
> If you define #method_missing, you'll also have to define respond_to?.
> It seems also necessary to define #== and a few other methods:
>
>     irb(main):001:0> BasicObject.instance_methods
>     => [:==, :equal?, :"!", :"!=", :__send__]

Or just use Delegator.

-- 
Rick DeNatale

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