From: Robert Klemme <bob.news@...>
Date: 2004-04-22T17:09:07+09:00
Subject: Re: Creating bang methods


"Gavin Kistner" <gavin@refinery.com> schrieb im Newsbeitrag
news:245541A6-93BD-11D8-A280-000A959CF5AC@refinery.com...
> On Apr 21, 2004, at 11:34 AM, Jon Hurst wrote:
> > [...] I would like to create bang methods of some math functions
> > (mostly abs), but I don't know how to modify the reciever in place
> > because the value of self cannot be changed.
>
> This problem bit me repeatedly. It's sort of a design feature, not a
> flaw, as I understand it.
>
> Certain base classes are not meant to be mutable, per the design of the
> language. The 'best' way to do this, I've been told, is what I did for
> my MutableTime class, to wit:
> a) Create a new class (that doesn't inherit from the other)
> b) Keep your own instance variable that is the base class
> c) When you need to modify the instance, swap out your instance,
> otherwise
> d) Pass method calls on to the instance.
>
> For example, something like
>
> class MyNumber
> def initialize( initialValue=nil )
> @n = initialValue || 0
> end

One check too much.

> def abs!
> @n = @n.abs
> end
>
> def method_missing(meth, *args, &block) # :nodoc:
> @n.send(meth, *args, &block)
> end

Those two can be combined.

> end

How about:

class MyNumber
  def initialize( initialValue = 0 )
    @n = initialValue
  end

  def method_missing(meth, *args, &block)
    if /\!$/ =~ meth.to_s
      @n = @n.send(meth.to_s[0...-1], *args, &block)
    else
      self.class.new @n.send(meth, *args, &block)
    end
  end

  # eql, == etc still missing here
end

x = MyNumber.new -10
p x
x.abs!
p x

Regards

    robert