From: Robert Dober <robert.dober@...>
Date: 2007-06-11T04:51:11+09:00
Subject: Re: fun with "case"

On 6/10/07, Marc Heiler <shevegen@linuxmail.org> wrote:
> If its fun, its nice :-)
> In ruby i also enjoy when its short and terse (if i manage to understand
> it) though :-)

Ok it is all Robert's fault, his idea is really nice, I will explain
Define a method on integers that will implement a === which will be
called for the arg in
  case arg

he just defines a proc on which he aliased :call to :=== (that is the
genius part of this, and having the idea of course)
irb(main):001:0> class Integer
irb(main):002:1>   def elements
irb(main):003:2>     cond = lambda {|enum| self == enum.size}
irb(main):004:2>     class <<cond
irb(main):005:3>       alias :=== :call
irb(main):006:3>     end
irb(main):007:2>     cond
irb(main):008:2>   end
irb(main):009:1> end
=> nil
irb(main):010:0> case [1,2,3]
irb(main):011:1> when 3.elements
Ruby will call 3.element === [1,2,3] as you know
But 3.elements is a proc with === aliased to :call, thus
Ruby calls this_proc.call([1,2,3])
in which [1,2,3].size will be compared to self whihc of course is 3.
<snip>
As I am very lazy I want to have a shortcut for "def elements..."
I just put a method in class Module which will define such methods.
...
   define_method name do
     | *args |
** is like "def #{name} *args"
     cond = lambda{ |x|
** literal code inside def
       trans ? self.send(trans, *args) == x.send( arg_mth ) :
## forget trans
         self == x.send( arg_mth )
## this part only is corresponding to Robert's code, arg_mth is :size
in our case
## that becomes equivalent ( but way slower ) to
** self == x.size
     }
     class << cond
       alias_method :===, :call
     end
     cond
** all above is just stolen from the original idea
   end

if you call that with :name=>"elements" and on => "size" it will just
do exactly what Robert did, forget the arguments extension, that was
just to fool around even more.
This is a little bit like macros in Lisp - just better, because I can
figure it out ;).

Cheers
Robert
-- 
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw