[ruby-core:90982] [Ruby trunk Feature#6240] Enumerable#drop with negative argument

[knu@ruby-lang.org]

Issue #6240 has been updated by knu (Akinori MUSHA).


Using an existing feature, `[1,2,3,4,5].lazy.drop(-n)` could be written as `[1,2,3,4,5].each_cons(n+1).lazy.map(&:first)`.
Enumerable#each_cons does not use a circular buffer, though. (It currently uses push & shift)

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Feature #6240: Enumerable#drop with negative argument
https://bugs.ruby-lang.org/issues/6240#change-76199

* Author: marcandre (Marc-Andre Lafortune)
* Status: Feedback
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
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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?



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