From: "shugo (Shugo Maeda)" <redmine@...>
Date: 2012-04-02T10:41:54+09:00
Subject: [ruby-core:44051] [ruby-trunk - Feature #6240] Enumerable#drop with negative argument


Issue #6240 has been updated by shugo (Shugo Maeda).


marcandre (Marc-Andre Lafortune) wrote:
> > How Enumerable#drop can know the total number of elements?
> > The source of elements might be IO.  Besides that, the total number of elements might be infinite.
> 
> `drop` would have to consume the whole iteration, indeed, which is why I was talking about a buffer. The buffer holds elements until we know they are not in the last (-n) elements. Here's a Ruby implementation:

Ah, I see.  It's interesting.

Do you have any use case in mind?

----------------------------------------
Feature #6240: Enumerable#drop with negative argument
https://bugs.ruby-lang.org/issues/6240#change-25581

Author: marcandre (Marc-Andre Lafortune)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0


Currently, Enumerable#drop works only for non-negative arguments.

It could be extended so that negative arguments means dropping from the end:

    [:hello, :world].drop(-1) # => [:hello]

This could especially be interesting for `Lazy#drop`, which would keep a circular buffer of elements before yielding them.

    (1..6).lazy.drop(-3).each{|x| puts x} # -> prints 1, 2 and 3

Thoughts?


-- 
http://bugs.ruby-lang.org/