From: ko1@... Date: 2019-07-30T07:30:40+00:00 Subject: [ruby-core:94028] [Ruby master Bug#15620] Block argument usage affects lambda semantic Issue #15620 has been updated by ko1 (Koichi Sasada). Assignee changed from matz (Yukihiro Matsumoto) to ko1 (Koichi Sasada) Status changed from Open to Assigned ---------------------------------------- Bug #15620: Block argument usage affects lambda semantic https://bugs.ruby-lang.org/issues/15620#change-80253 * Author: alanwu (Alan Wu) * Status: Assigned * Priority: Normal * Assignee: ko1 (Koichi Sasada) * Target version: * ruby -v: * Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN ---------------------------------------- The following snippet demonstrate the issue: ``` ruby def pass_after_use(&block) raise unless block lambda(&block).call end def direct_pass(&block) lambda(&block).call end pass_after_use do |_arg| puts "fine, because block is materialized into a Proc before it is passed to #lambda" end direct_pass do |_arg| puts "Raises because all args are required. This is not printed" end ``` Output: ``` fine, because block is materialized into a Proc before it is passed to #lambda Traceback (most recent call last): 2: from lambda-block-pass.rb:14:in `<main>' 1: from lambda-block-pass.rb:7:in `direct_pass' lambda-block-pass.rb:14:in `block in <main>': wrong number of arguments (given 0, expected 1) (ArgumentError) ``` I think having the line `raise unless block` affect `Kenrel#lambda`'s semantic is pretty surprising. Note that if I do `raise unless block_given?`, call to the lambda without arg also raises. If I was to decide, I would always have the resulting lambda have required arguments even after multiple levels of block pass. That is, as long as the original block is a literal block. This is either a breaking change or a regression from 2.4. The same script executes without raising in 2.4.5 (block arguments are always materialized). -- https://bugs.ruby-lang.org/ Unsubscribe: <mailto:ruby-core-request@ruby-lang.org?subject=unsubscribe> <http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>