From: Ross Bamford <rossrt@...>
Date: 2006-06-02T09:17:16+09:00
Subject: Re: Adding an Increment Operator?

On Fri, 2006-06-02 at 08:15 +0900, Dave Howell wrote:
> As Logan pointed out in a different thread:
> 
> > % cat increment.rb
> > class Fixnum
> >   def increment
> >     self = self + 1
> >   end
> > end
> >
> > a = 1
> > a.increment
> >
> >
> > % ruby increment.rb
> > -:13: Can't change the value of self
> >     self = self + 1
> >           ^
> 
> So, how WOULD I create an .increment operator? I get why I can't put it 
> in class Fixnum (well, I think I know why); Fixnums are symbol-ish-ly 
> unalterable. 5.increment should fail, for sanity's sake.

Depending on what you want to do, maybe you could cheat:

require 'delegate'

class Fixbox < DelegateClass(Fixnum)
  def self.[](num); new(num); end
  def decrement; __getobj__ - 1; end
  def decrement!; __setobj__(decrement); end
  def increment; __getobj__ + 1; end
  def increment!; __setobj__(increment); end
end

f = Fixbox[3]
# => 3
f.increment!
# => 4
f
# => 4
f.decrement!
# => 3
f
# => 3

:)

-- 
Ross Bamford - rosco@roscopeco.REMOVE.co.uk