rubocop / rubocop/ruby-style-guide

Style guide: misleading description for "Slicing with Ranges"

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Description

In the style guide under Slicing with Ranges it's said that

[0..-1] in ary[0..-1] is redundant and simply synonymous with ary.

However, one makes a shallow copy while the other doesn't:

ary = [1, 2, 3]
with_slice = ary[0..-1]
without_slice = ary
ary[0] = :changed

# [1, 2, 3]
puts with_slice.inspect

# [:changed, 2, 3]
puts without_slice.inspect

By analogy to the Python idiom ary[:], I would guess that the "bad" form is often written specifically to make a copy rather than an alias.

I suggest that the advice be changed to say something like ary.clone, ary.dup or [*ary] is preferred (whatever is considered better style), or that simply ary is preferred if a copy isn't needed. If clone is a good alternative then it's worth adding that it isn't exactly synonymous with a full slice, since even ary.clone(freeze: false) clones the singleton class, whereas slicing doesn't.

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked Style guide section, “Slicing with Ranges,” and verify the distinction between ary[0..-1] and ary using the examples in the issue. Update the guidance to distinguish copying from aliasing and state whether ary.clone, ary.dup, [*ary], or simply ary is preferred, including the noted singleton-class caveat if clone is recommended.

Written by the indexing model from the issue text.

Assessment

Tech stack
ruby
Domain
documentation
Issue type
Documentation
Difficulty
2/5
Estimated time
1-3 hours
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
48/100

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