Issue #19777 has been reported by alanwu (Alan Wu). ---------------------------------------- Feature #19777: Make `Kernel#lambda` raise when called without a literal block https://bugs.ruby-lang.org/issues/19777 * Author: alanwu (Alan Wu) * Status: Open * Priority: Normal ---------------------------------------- Since 3.0.0, released in 2020, calling `Kernel#lambda` without a literal block has been issuing a deprecation warning: ```ruby Warning[:deprecated] = true def foo(&b) lambda(&b) end foo {} # => test.rb:2: warning: lambda without a literal block is deprecated; use the proc without lambda instead ``` I think enough time has passed and we should make it raise in all situations where it currently issues a deprecation warning. The original decision to deprecate is here: https://bugs.ruby-lang.org/issues/15973#note-46 The new behavior allows one to predict whether `Kernel#lambda` will return by inspecting its direct caller, checking whether the call site has a literal block. It will remove some hard-to-predict cases where `Kernel#lambda` receives a non-literal block forwarded with `super` or `rb_funcall_passing_block`. The method will always return a lambda, if it returns. However, note that `send` will be a special exception in this new model: ```ruby Warning[:deprecated] = true singleton_class.send(:public, :lambda) p (send(:lambda) {}).lambda? # => true without warning p (public_send(:lambda) {}).lambda? # => true with warning, would raise instead ``` This newer model is friendlier to some optimization we're investigating for YJIT as it has fewer moving parts. -- https://bugs.ruby-lang.org/