Using [] with the Safe Navigation Operator in Ruby

Question

I currently have a piece of code that looks like:

if match = request.path.match(/\A\/(?<slug>(?!admin|assets)\w+)/)
  match[:slug]
end

Is there a way to use the safe navigation operator (introduced in 2.3.0) to avoid this if conditional?

Use `fetch[:slug]`? Or just use safe-nav and `[]` (don't know if that'll work)? Personally I think it's hard to read already, and that'll just make it worse. — Dave Newton, Jan 14 '16 at 16:33
@DaveNewton can't use `fetch` here because `match` returns `nil` in the case the regex didn't match. Also open to suggestions on how to make this more readable. — Kyle Decot, Jan 14 '16 at 18:16
`match` returns `MatchData` on success, it does not have `fetch` method like hash does — Vasfed, Jan 14 '16 at 19:06

score 67 · Accepted Answer · answered Jan 14 '16 at 16:46

67

Just use the ordinary (non-sugar) form.

request.path.match(/\A\/(?<slug>(?!admin|assets)\w+)/)&.[](:slug)

answered Jan 14 '16 at 16:46

sawa

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I think the `&.[](:slug)` part is what I was doing wrong. I had previously been trying `&.[:slug]` – Kyle Decot Jan 14 '16 at 16:52
4

@KyleDecot Yep, this is what I mean with the `[]` bit although I think it's just horrendous to look at. – Dave Newton Jan 14 '16 at 18:58

score 23 · Answer 2 · answered Jul 06 '17 at 09:29

23

For better readability I would pick #dig instead of the #[].

Like,

request.path.match(/\A\/(?<slug>(?!admin|assets)\w+)/)&.dig(:slug)

instead of

request.path.match(/\A\/(?<slug>(?!admin|assets)\w+)/)&.[](:slug)

answered Jul 06 '17 at 09:29

Vedant Agarwala

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Interesting idea, but I get "undefined method 'dig' for MatchData", even with ruby 2.4.2 and rails 5.1.4. – Anson Sep 18 '17 at 13:46
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The dig method is for hashes. While it also works on arrays, it looks like MatchData doesn't fully implement the array interface. Since the safe navigation operator works like #try! instead of #try, only the second version works. https://stackoverflow.com/a/45825498 – Kingdon May 31 '18 at 19:06

score 8 · Answer 3 · answered Jul 14 '18 at 15:53

8

For readability, I prefer using the match's named_captures method which is available from ruby 1.9.1, with the safe operator which is available from ruby 2.3.0.

request.path.match(/\A\/(?<slug>(?!admin|assets)\w+)/)&.named_captures&.dig('slug')

answered Jul 14 '18 at 15:53

Mike State

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score 4 · Answer 4 · answered Jan 14 '16 at 16:36

4

You can send any method, so using safe-browsing operator this will be:

request.path.match(/\A\/(?<slug>(?!admin|assets)\w+)/)&.send(:[], :slug)

answered Jan 14 '16 at 16:36

Vasfed

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This definitely works but I went w/ the approach of using `&.[](:slug)`. Thanks for looking into it though! – Kyle Decot Jan 14 '16 at 17:00

Using [] with the Safe Navigation Operator in Ruby

4 Answers4