From: Rein Henrichs <reinh@...>
Date: 2010-06-08T02:10:06+09:00
Subject: Re: inject method of Array class

On 2010-06-07 06:08:39 -0700, David A. Black said:

> Hi --
> 
> On Mon, 7 Jun 2010, Robert Klemme wrote:
> 
>> 2010/6/7 David A. Black <dblack@rubypal.com>:
>> 
>>> On Mon, 7 Jun 2010, Rein Henrichs wrote:
>>> 
>>>> On 2010-06-06 17:55:58 -0700, David A. Black said:
>> 
>>>> I suspect that the majority are overwritten for performance reasons,
>>>> although some of them surprise me as well.
>>>> 
>>>> A linked list, for instance, would have a constant time #count because
>>>> that state is kept on the list object and doesn't require an O(n)
>>>> enumeration of the members.
>>> 
>>> I think it's a mixture of performance reasons and things like what it
>>> should return if there's no block (like Enumerable#map always
>>> returning an array vs. Array#map returning its receiver). Array is
>>> definitely the one that has the most overrides, with Hash coming in
>>> second at 6 and IO having none.
>> 
>> David, I guess you meant to write "... vs. Array#map! returning its
>> receiver"?  Note the exclamation mark.  Array#map returns a new Array
>> on every invocation.
> 
> I really meant to say a copy of its receiver -- I was looking at this:
> 
>      if (!rb_block_given_p()) {
>          return rb_ary_new4(RARRAY(ary)->len, RARRAY(ary)->ptr);
>      }
> 
> from array.c.
> 
> 
> David

Indeed. The Rubinius implementations of these Array methods are quite 
revealing. It is easy to see the difference between them and their 
Enumerable counterparts.

-- 
Rein Henrichs
http://puppetlabs.com
http://reinh.com