Issue #19538 has been updated by mame (Yusuke Endoh). @matz (and @ko1, @shyouhei, and @nobu) also said that `ruby -w` should not enable this warning mode. `ruby -W:performance` should do. ---------------------------------------- Feature #19538: Performance warnings https://bugs.ruby-lang.org/issues/19538#change-102759 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal ---------------------------------------- Suggested by @Eregon. There are program behaviors that are supported, but that we know aren't good for performance, however it's hard for users to know about them. Now that we have warning categories, we could add a `:performance` category to allow the VM to emit warning in some situations. The category would be disabled by default, and users interested in optimizing their program could turn it on in development. ```ruby Warning[:performance] = true ``` -- https://bugs.ruby-lang.org/