From: Mauricio Fernandez <mfp@...>
Date: 2006-08-13T19:03:43+09:00
Subject: Re: A use case for an ordered hash

On Sun, Aug 13, 2006 at 06:31:07PM +0900, Matt Todd wrote:
> Absolutely... an Array is perfect for ordered information.
> 
> actions = [
>  { /abcd/ => lambda { do_this } },
>  { /xyz/ => lambda { do_that } },
>  { /abc/ => lambda { other } }
> ]
> 
> Then, all you do is...
> 
> actions.select { |action| action[input] }
> 
> where input = /xyz/ you will receive the appropriate hash (key and
> Proc) in an array. So, to do something with that, you could...
> 
> actions.select { |action| action[input] }.first[input].call
> 
> which calls the Proc associated with the matching element.

That's not what he wants though (the point is matching against the Regexp ---
Hash#[] doesn't buy you anything there).

Maybe

require 'enumerator'
def ASSOC(x); x.enum_for(:each_slice, 2).to_a end

actions = ASSOC [
  /abcd/,  lambda{ 1 },
  /xyz/,   lambda{ 2 },
  /abc/,   lambda{ 3 }
]

# Then he's got to

def run(command, actions)
  actions.each{|re, action| return action[command] if re =~ command}
  nil
end

run("abcdef", actions)            # => 1
run("abcf", actions)              # => 3


# But  this would be nicer
class Array
  def cassoc(x)  # "case assoc"
    each{|arr| return arr if arr[0] === x}
    nil
  end
end

re, action = actions.cassoc("abcdef")
action and action.call                             # => 1
re, action = actions.cassoc("abcx")
action and action.call                             # => 3


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