Feature #15918

Pattern matching for Set

Added by marcandre (Marc-Andre Lafortune) about 1 month ago. Updated about 1 month ago.

Target version:


Currently, Set does not respond to deconstruct. Shouldn't we implement it using to_a?

require 'set'
case Set[1, 2, 3]
in [1, 2, 3]
  p "match"
  p "no match"
# => "no match", should be "match"

Related issues

Related to Ruby master - Feature #14912: Introduce pattern matching syntaxAssignedActions


Updated by Eregon (Benoit Daloze) about 1 month ago

Did you mean in Set[1, 2, 3] ?

Updated by marcandre (Marc-Andre Lafortune) about 1 month ago

Eregon (Benoit Daloze) wrote:

Did you mean in Set[1, 2, 3] ?

I didn't, but it should match too; it's the same as my example but with the added constraint that the object should be a descendant a Set. Note that in Set[1, 2, 3] does not call Set.[](1, 2, 3)...

Updated by jeremyevans0 (Jeremy Evans) about 1 month ago

Sets are supposed to be unordered (any ordering is an implementation detail). If Set[1, 2, 3] matches in your example, so should Set[3, 2, 1], since Set[1, 2, 3] == Set[3, 2, 1]. We could attempt to sort the elements of the set before pattern matching, but some sets contain unsortable elements (e.g. elements of different types). If pattern matching can work correctly when using in Set[...], then maybe this would be desirable, but I'm not sure if that is possible.

To answer your question, in my opinion, yes, we shouldn't implement deconstruct using to_a.


Updated by jeremyevans0 (Jeremy Evans) about 1 month ago

  • Backport deleted (2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN)
  • Tracker changed from Bug to Feature

Updated by ktsj (Kazuki Tsujimoto) about 1 month ago

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