From: "zverok (Victor Shepelev) via ruby-core" <ruby-core@...>
Date: 2024-07-14T11:33:33+00:00
Subject: [ruby-core:118590] [Ruby master Feature#17279] Allow a negative step in Range#step with a block

Issue #17279 has been updated by zverok (Victor Shepelev).


FWIW, my PR with adjusting `Range#step` behavior fixes this, too: https://github.com/ruby/ruby/pull/7444 (as part of the unificatioin/simplification process):

>From the PR description:

> Consistent support for negative step:

```ruby
p (1..-10).step(-3).to_a 
#=> [1, -2, -5, -8] -- ArithmeticSequence backward iteration, on Ruby 3.3 and my code
(1..-10).step(-3) { p _1 }
# Ruby 3.3: step can't be negative (ArgumentError) -- inconsistent with ArithmeticSequence behavior
# my code: prints 1, -2, -5, -8, consistent with ArithmeticSequence
```

----------------------------------------
Feature #17279: Allow a negative step in Range#step with a block
https://bugs.ruby-lang.org/issues/17279#change-109117

* Author: mrkn (Kenta Murata)
* Status: Assigned
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
`Range#step` prohibits a negative step when a block is given.

```
>> (6..3).step(-1) {|i| p i }
Traceback (most recent call last):
        5: from /home/mrkn/.rbenv/versions/2.7/bin/irb:23:in `<main>'
        4: from /home/mrkn/.rbenv/versions/2.7/bin/irb:23:in `load'
        3: from /home/mrkn/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/irb-1.2.4/exe/irb:11:in `<top (required)>'
        2: from (irb):1
        1: from (irb):1:in `step'
ArgumentError (step can't be negative)
```

But `Range#step` allows a negative step when it is called without a block.  In this case, `Range#step` creates an ArithmeticSequence, and `ArithmeticSequence#each` can iterate with a negative step.

```
>> (6..3).step(-1).each {|i| p i }
6
5
4
3
=> ((6..3).step(-1))
```

I think the prohibition of a negative step in `Range#step` has already been meaningless, so it may be better to permit it for consistency.



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