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Feature #7546

open

Change behavior of `Array#slice` for an argument of `Range` class

Added by alexeymuranov (Alexey Muranov) over 11 years ago. Updated over 3 years ago.

Status:
Open
Target version:
-
[ruby-core:50771]

Description

=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.)

  1. (({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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