Issue #19840 has been updated by mame (Yusuke Endoh). Assignee set to ktsj (Kazuki Tsujimoto) ---------------------------------------- Feature #19840: [Proposal] Expand Find pattern to Multiple Find https://bugs.ruby-lang.org/issues/19840#change-104518 * Author: FlickGradley (Nick Bradley) * Status: Open * Priority: Normal * Assignee: ktsj (Kazuki Tsujimoto) ---------------------------------------- Hello! I love Ruby's pattern matching features. I would like to propose an expansion of the Find pattern which allows the selection of multiple matching elements of an array. I often find myself dealing with data like this: ``` ruby { results: [{ id: 1, name: "foo" }, { id: 2, name: "bar" }, ... ] } ``` My problem is that I need to retrieve all the `id` values from the nested array of hashes, and I don't know how many there will be in advance. It seems that the Find pattern could be expanded from allowing `pattern` (matching a single element) to `*pattern`. Examples: ``` ruby # Base case case { results: [{ id: 1, name: "foo" }, { id: 2, name: "bar" }] } in results: [*{ id: ids }] "matched: #{ids}" else "not matched" end #=> matched: [1, 2] # With * at the end (rest of args) - same result case { results: [{ id: 1, name: "foo" }, { id: 2, name: "bar" }] } in results: [*{ id: ids }, *] "matched: #{ids}" else "not matched" end #=> matched: [1, 2] # When one element doesn't match and there is no *rest case { results: [{ name: "foo" }, { id: 2, name: "bar" }] } in results: [*{ id: ids }] "matched: #{ids}" else "not matched" end #=> not matched ``` Similarly, `*Constant` could work to pull out types with an As pattern: ``` ruby case [1, 2, 3, "string"] in *Integer => nums, * "matched: #{nums}" else "not matched" end #=> matched: [1, 2, 3] ``` Other patterns would work in the same way. Essentially, this expands the concept of `*` in pattern matching to mean "a variable number of `things matching subpattern`". Today, the only pattern supported by `*` is a variable binding - but it could be any of the other subpatterns as well. This proposal does imply that this would work: ``` ruby a = 2 [1, 2, 2, 3] in [*, *^a, *] #=> true ``` To me, the `*` represents the variable number of matches, so the syntax makes intuitive sense. But others may have different opinions about `*^` being adjacent. It may also imply this would work, though we could restrict the number of non-variable patterns (in other words, patterns that have the possibility of not matching) to 1 per Array so that this isn't possible.. I'm not sure something like this would be useful or clear. ``` ruby a = 2 [1, 2, "hello", "ruby"] in [*Integer, *String] #=> true ``` This feature feels like the missing piece of the Find pattern to me - I often want to "Find Multiple". If others agree, I would be happy to contribute by working on this feature and creating a pull request. -- https://bugs.ruby-lang.org/