Issue #19107 has been updated by k0kubun (Takashi Kokubun). I second this proposal. `def foo(bar:,)` doesn't seem like a real use-case, but when a method has so many arguments and I declare arguments in multiple lines, I would love to put a trailing comma to minimize future git diff and make reviewing the Ruby code easier. For example, this is today's `ERB#initialize`: ```rb def initialize(str, safe_level=NOT_GIVEN, legacy_trim_mode=NOT_GIVEN, legacy_eoutvar=NOT_GIVEN, trim_mode: nil, eoutvar: '_erbout') # ... end ``` This line is still short enough to fit on my screen, however, if we were to add another option, e.g. `filename`, I would write: ```rb def initialize( str, safe_level=NOT_GIVEN, legacy_trim_mode=NOT_GIVEN, legacy_eoutvar=NOT_GIVEN, trim_mode: nil, eoutvar: '_erbout', filename: nil, ) # ... end ``` which doesn't seem awkward to me. But this is a SyntaxError today. If you don't put a `,` there, you'll see a diff on `filename` when you add another option after that even if the patch is not related to `filename`, which would make me frustrated when reviewing that code. ---------------------------------------- Feature #19107: Allow trailing comma in method signature https://bugs.ruby-lang.org/issues/19107#change-101836 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal ---------------------------------------- A popular style for multiline arrays, hashes or method calls, is to use trailing commas: ```ruby array = [ 1, 2, 3, ] hash = { foo: 1, bar: 2, baz: 3, } Some.method( 1, 2, foo: 3, ) ``` The main reason to do this is to avoid unnecessary noise when adding one extra element: ```diff diff --git a/foo.rb b/foo.rb index b2689a7e4f..ddb7dc3552 100644 --- a/foo.rb +++ b/foo.rb @@ -1,4 +1,5 @@ Foo.bar( foo: 1, - bar: 2 + bar: 2, + baz: 3 ) ``` However, this pattern doesn't work with method declarations: ```ruby def foo(bar:,) # syntax error, unexpected ')' ``` ### Proposal For consistency and convenience I propose to allow trailing commas in method declarations. -- https://bugs.ruby-lang.org/