Issue #18966 has been updated by fcheung (Frederick Cheung). Ruby 3.2.2 exhibits the same behaviour as above but on master ( as of b1f345b1 ) all of these now evaluate to 'a' ---------------------------------------- Bug #18966: Strange behavior when numbered parameters and method definition are both used in a block https://bugs.ruby-lang.org/issues/18966#change-105320 * Author: tompng (tomoya ishida) * Status: Open * Priority: Normal * ruby -v: ruby 3.2.0dev (2022-08-19T04:20:20Z :detached: 17d0e5bee7) [x86_64-linux] * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN ---------------------------------------- ~~~ruby 'a'.tap { p _1; def f()=42 } #=> "a" 'a'.tap { p _1; def f(a)=42 } #=> nil 'a'.tap { def f()=42; p _1 } #=> "a" 'a'.tap { def f(a)=42; p _1 } # Syntax Error -:1: ordinary parameter is defined ~~~ -- https://bugs.ruby-lang.org/