Bug #21184: SyntaxError when combining `in` with inline hash-rocket (`=>`)

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-linux]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[jtannas (Joel Tannas)]

I believe the following should be valid syntax but it's throwing a SyntaxError:

{ a: 1 } in { a: 1 } # => true
{ a: 1 } in { a: Integer } # => true
pattern = { "a" => 1 }; { "a" => 1 } in pattern # => true
{ "a" => 1 } in { "a" => 1 } # => SYNTAX ERROR

[alanwu (Alan Wu)]

• Status changed from Open to Rejected

It's working as documented

Note that only symbol keys are supported for hash patterns.

By the way, the third line that uses in uses a wildcard pattern so is essentially assigning to pattern:

irb(main):003> pattern = { "a" => 1 }; 0 in pattern
=> true
irb(main):004> p pattern
0

[jtannas (Joel Tannas)]

Thank you for the prompt reply Alan.
Sorry I missed that line while skimming through that document prior to submitting.

I think I need to do some more reading up on the => operator.