From: Mauricio Fernandez <mfp@...>
Date: 2006-08-14T01:16:14+09:00
Subject: Re: A use case for an ordered hash

On Mon, Aug 14, 2006 at 12:27:07AM +0900, James Edward Gray II wrote:
> On Aug 13, 2006, at 3:25 AM, Robert Klemme wrote:
> >Hal Fulton wrote:
> >>Once I wanted a "dynamic case statement" of sorts.
> >>I wanted to use procs as values in a hash. Something
> >>like:
> >>   actions = { /abcd/  => lambda { do_this },
> >>               /xyz/   => lambda { do_that },
> >>               /abc/   => lambda { other }}
[...]
> >To me a Hash feels wrong.  Why?  Because you don't make any use of  
> >hash properties for fast lookup.  You just iterate in plain order.
> 
> He *is* making use of a Hash property.  He wants the keys to be  
> unique.  None of the other solutions shown in this thread have  
> addressed that.

Hal is making the case for *literal* "ordered hashes".  The keys will be
unique because he's writing them himself manually. I don't think he wants to
make use of this:

actions = { /a/ => 1,  #  <--
            /b/ => 2,  #     \
	    /a/ => 4   #  <--+--  why do this in the first place.
	  }
actions[/a/]                       # => 4

The way he uses the structure is reminiscent of Array#assoc. The only thing
a Hash has going for it in this case is the cleaner notation and the arrow.
But  
    actions = ASSOC [/abcd/, lambda{ ... }, 
		     /abc/,  lambda{ ... } ] 
(using parentheses if you want) looks good enough for me, and something like 
the Array#cassoc I showed before would do fine in this case.

-- 
Mauricio Fernandez  -   http://eigenclass.org   -  singular Ruby