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List: ruby-core
Subject: [ruby-core:108127] [Ruby master Bug#18247] weird results for `Array#slice` or `Array#[]` with argume
From: "jeremyevans0 (Jeremy Evans)" <noreply () ruby-lang ! org>
Date: 2022-03-30 23:05:44
Message-ID: redmine.journal-97101.20220330230544.51932 () ruby-lang ! org
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Issue #18247 has been updated by jeremyevans0 (Jeremy Evans).
This is still an issue in the master branch. I've submitted a pull request to fix \
it: https://github.com/ruby/ruby/pull/5739
----------------------------------------
Bug #18247: weird results for `Array#slice` or `Array#[]` with argument of type \
`Enumerator::ArithmeticSequence` https://bugs.ruby-lang.org/issues/18247#change-97101
* Author: lxxxvi (Mario Schüttel)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
There are weird results for `Array#slice` or `Array#[]` with argument of type \
`Enumerator::ArithmeticSequence`.
Particularly most results with negative steps are weird. For example:
```ruby
@array = [0, 1, 2, 3, 4, 5]
@array.slice((2..).step(-1)) # => [2, 1, 0]
@array.slice((2..).step(-2)) # => [2, 0]
@array.slice((2..).step(-3)) # => [2]
@array.slice((2..).step(-4)) # => [0] # ??? I'd have expected \
[2]
@array.slice((-3..).step(-1)) # => [3, 2, 1, 0]
@array.slice((-3..).step(-2)) # => [3, 1]
@array.slice((-3..).step(-3)) # => [3, 0]
@array.slice((-3..).step(-4)) # => [3]
@array.slice((-3..).step(-5)) # => [0] # ??? I'd have expected \
[3] ```
Have a look at these examples with "beginless" ranges and negative steps.
Particularly the ones exluding the end value (`...`) seem wrong:
```ruby
@array = [0, 1, 2, 3, 4, 5]
## end with zero index
@array.slice((..0).step(-1)) # => [5, 4, 3, 2, 1, 0]
@array.slice((...0).step(-1)) # => [5, 4, 3, 2, 1, 0]
@array.slice((..0).step(-2)) # => [5, 3, 1]
@array.slice((...0).step(-2)) # => [5, 3, 1]
@array.slice((..0).step(-10)) # => [0]
@array.slice((...0).step(-10)) # => [0]
## end with positive index
@array.slice((..3).step(-1)) # => [5, 4, 3]
@array.slice((...3).step(-1)) # => [5, 4, 3]
@array.slice((..3).step(-2)) # => [5, 3]
@array.slice((...3).step(-2)) # => [5, 3]
@array.slice((..3).step(-10)) # => [3]
@array.slice((...3).step(-10)) # => [3]
## end with negative index
@array.slice((..-2).step(-1)) # => [5, 4]
@array.slice((...-2).step(-1)) # => [5, 4]
@array.slice((..-2).step(-2)) # => [5]
@array.slice((...-2).step(-2)) # => [5]
@array.slice((..-2).step(-10)) # => [4]
@array.slice((...-2).step(-10)) # => [4]
```
Finally, some examples where the range is "inverted".
Particularly, the results for the ones excluding the end value (`...`) look strange.
But all examples seem weird, but I might not understand the concept of arithmetic \
sequence in depth.
```ruby
@array = [0, 1, 2, 3, 4, 5]
# start and end with positive index
@array.slice((3..1).step(-1)) # => [3, 2, 1]
@array.slice((3...1).step(-1)) # => [2, 1]
@array.slice((3..1).step(-2)) # => [3, 1]
@array.slice((3...1).step(-2)) # => [2]
@array.slice((3..1).step(-10)) # => [1]
@array.slice((3...1).step(-10)) # => [1]
# start with negative index, end with positive index
@array.slice((-2..1).step(-1)) # => [4, 3, 2, 1]
@array.slice((-2...1).step(-1)) # => [3, 2, 1]
@array.slice((-2..1).step(-2)) # => [4, 2]
@array.slice((-2...1).step(-2)) # => [3, 1]
@array.slice((-2..1).step(-10)) # => [1]
@array.slice((-2...1).step(-10)) # => [1]
# start with positive index, end with negative index
@array.slice((4..-4).step(-1)) # => [4, 3, 2]
@array.slice((4...-4).step(-1)) # => [3, 2]
@array.slice((4..-4).step(-2)) # => [4, 2]
@array.slice((4...-4).step(-2)) # => [3]
@array.slice((4..-4).step(-10)) # => [2]
@array.slice((4...-4).step(-10)) # => [2]
# start with negative index, end with negative index
@array.slice((-2..-4).step(-1)) # => [4, 3, 2]
@array.slice((-2...-4).step(-1)) # => [3, 2]
@array.slice((-2..-4).step(-2)) # => [4, 2]
@array.slice((-2...-4).step(-2)) # => [3]
@array.slice((-2..-4).step(-10)) # => [2]
@array.slice((-2...-4).step(-10)) # => [2]
```
Found while writing specs for this method in https://github.com/ruby/spec/pull/857
--
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