From: "David A. Black" <dblack@...>
Date: 2009-07-29T21:31:46+09:00
Subject: Re: previous value in array block

Hi --

On Wed, 29 Jul 2009, Robert Dober wrote:

> 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)
>   ...

I confess I don't see the point, but thanks for clarifying.


David

-- 
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