Issue #19150 has been updated by mame (Yusuke Endoh). https://github.com/ruby/ruby/pull/6948 ---------------------------------------- Bug #19150: pack/unpack silently ignores unknown directives https://bugs.ruby-lang.org/issues/19150#change-100696 * Author: Eregon (Benoit Daloze) * Status: Open * Priority: Normal * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN ---------------------------------------- But I believe it should be an error instead. Typically when a parser sees a syntax error it should fail not continue silently. For instance `[1].pack('<L')` succeeds and only emits a warning if `$VERBOSE` is true. This behavior caused confusion in https://github.com/oracle/truffleruby/issues/2791 I think it should fail with an `ArgumentError` instead. Extracted from https://bugs.ruby-lang.org/issues/19108#note-3 -- https://bugs.ruby-lang.org/