From: Robert Klemme <shortcutter@...>
Date: 2008-03-26T21:12:43+09:00
Subject: Re: Passing params to Map method

2008/3/26, Ruby Freak <twscannell@gmail.com>:

>  What I think is happening is the new "Info.properties" accessor is
>  cleverly leveraging self.property as a method to both set a new
>  property into @@properties and to return (yield) just the name when
>  the parameter passed to the code block is just the first half of the
>  array (name, ). Just understanding that after 8 months and thousands
>  of hours and reading thousands of pages of books is really exciting
>  for me.

Yep.  Methods #names and #values_for are defined for the one instance
of Array only that is referenced by @@properties.  So these are not
general methods.  But they rely on methods defined in Array and
Enumerable to do their job.  Basically they seem to rely on the fact
that @@properties contains arrays with exactly two elements - the
first one used as property name and the second one as property value.
During iteration (i.e. map, find) on the array only the first is
assigned a block parameter (small optimization because the second one
is not needed).  That's it basically.  This is the usual pattern
matching that Ruby applies to multiple assignments:

irb(main):001:0> (a,(b,c),d)=1,2,3,4,5
=> [1, 2, 3, 4, 5]
irb(main):002:0> a
=> 1
irb(main):003:0> b
=> 2
irb(main):004:0> c
=> nil
irb(main):005:0> d
=> 3
irb(main):006:0> (a,(b,c),d)=1,[2,3],4,5
=> [1, [2, 3], 4, 5]
irb(main):007:0> a
=> 1
irb(main):008:0> b
=> 2
irb(main):009:0> c
=> 3
irb(main):010:0> d
=> 4

What makes this a bit hard to read is that assignment to @@properties
and the class<<@@properties are lumped into one statement.

>  I am a little iffy on the "class << (@@properties = [])" opening up
>  the Array object, but it fits the rule.(class << object)
>
>  if that is true, it is pretty cool code. (it's pretty cool even if I
>  am wrong) Ruby has quite a learning curve, especially for a VB guy.

Yeah, it seems VB is a bad place to start learning to program. :-)

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end