From: Robert Dober <robert.dober@...>
Date: 2009-07-29T21:21:40+09:00
Subject: Re: previous value in array block

On Wed, Jul 29, 2009 at 2:16 PM, David A. Black<dblack@rubypal.com> wrote:
> Hi --
>
> On Wed, 29 Jul 2009, Robert Dober wrote:
>
>> On Wed, Jul 29, 2009 at 10:50 AM, Xavier Noria<fxn@hashref.com> wrote:
>>>
>>> each_cons seems natural here:
>>>
>>> require 'enumerator'
>>>
>>> a = [1, 3, 3, 2]
>>> b = a[0, 1]
>>>
>>> a.each_cons(2) { |x, y| b << y - x }
>>
>> and purely functional
>> ( [0] + a ).each_cons( 2 ).map{ |x,y| y -x }
>> or with Tom's map arity trick implemented
>> ( [0] + a ).map{ | x, y | y - x }
>
> I don't understand that last one. Is this some kind of override of map
> that turns it into each_cons + map?
IIRC it was like this

module Enumerable
   method_alias :__map__, map
   def map &blk
      return __map__(&blk) if blk.arity < 2
      each_cons( blk.arity).map(&blk)
   ...

Robert
>
>
> David
>
> --
> David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
> Q: What's the best way to get a really solid knowledge of Ruby?
> A: Come to our Ruby training in Edison, New Jersey, September 14-17!
>   Instructors: David A. Black and Erik Kastner
>   More info and registration: http://rubyurl.com/vmzN
>
>



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