From: "drbrain (Eric Hodel)" <drbrain@...7.net>
Date: 2012-12-12T01:51:23+09:00
Subject: [ruby-core:50777] [ruby-trunk - Feature #7546] Change behavior of `Array#slice` for an argument of `Range` class


Issue #7546 has been updated by drbrain (Eric Hodel).

Target version set to Next Major

This will break existing code so I set it to next major.
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Feature #7546: Change behavior of `Array#slice` for an argument of `Range` class
https://bugs.ruby-lang.org/issues/7546#change-34627

Author: alexeymuranov (Alexey Muranov)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: Next Major


=begin
This is a concrete proposal to "fix" #4541.

It is also related to #7545.
For this proposal to make good sense, i think it would be nice if #7545 was at least partially accepted.

=== Main proposal

I propose (({Array#slice})) with (({Range})) type argument to work as follows:

  a = ['0', '1', '2', '3']
  a[1..2]   # => ['1', '2']
  a[-2..-1] # => ['2', '3']
  a[2..1]   # => ['2', '1']
  a[-1..-2] # => ['3', '2']
  a[-1..1]  # => ['3', '0', '1']
  a[1..-1]  # => ['1', '0', '3']
  a[1..1]   # => ['1']
  a[1...1]  # => []
  a[4..4]   # => [nil]
  a[4...4]  # => []
  a[9..9]   # => [nil]
  a[9...9]  # => []
  a[1..5]   # => ['1', '2', '3', nil, nil]

=== Secondary proposal: consider adding new instance methods to (({Array})) to compensate the changed behavior of (({Array#slice}))

If this proposal is accepted, the code "(({a[1..-2]}))" for an array (({a})) will not work as before.
This can be compensated by adding new instance methods to (({Array})).
For example the following ones.

1. (({Array#clip(fixnum, fixnum)})):

  ['0', '1', '2', '3'].clip(1, 1) # => ['1', '2']

Thus (({a.clip(1, 1)})) would be a replacement for (({a[1..-2]})).

(It looks strange to have to convert a pair of numbers ((*m*)) and ((*n*)) into a range (({m..(-1-n)})) to simply ask an array to remove ((*m*)) elements from the beginning and ((*n*)) elements from the end.
If #7545 is accepted, then the "(({a[1..-2]}))" syntax for "clipping" an array will make not much sense and maybe will not be possible.)

2. (({Array#from(fixnum)})), (({Array#till(fixnum)})):

  a = ['0', '1', '2', '3']
  a.from(1)          # => ['1', '2', '3']
  a.till(1)          # => ['0', '1']
  a.from(1).till(-2) # => ['1', '2']

In fact, in ((*Rails*)) (({ActiveSupport})) there are methods (({Array#from})) and (({Array#to})) like this, but unfortunately they do not accept negative indices.

((*Remark*)).  It would also be possible to have (({Array#clip!})), (({Array#from!})), (({Array#till!})).
=end



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