From: alex@... Date: 2014-03-13T14:53:05+00:00 Subject: [ruby-core:61470] [ruby-trunk - Bug #9605] Chaining "each_with_index.detect &lambda" raises ArgumentError Issue #9605 has been updated by Alex Rothenberg. If I understand correctly what you're saying is that it would behave as below. ~~~ plus = ->(x,y) {puts x+y} ~~~ 1. This would continue to work as it does today ~~~ def test yield 1,2 end test(&plus) # prints 3 ~~~ 2. The new behavior ~~~ def test yield [1,2] end test(&plus) # prints 3 ~~~ 3. Existing ArgumentError ~~~ def test yield 1,2,3 end test(&plus) # Would raise ArgumentError 3 for 2 ~~~ 4. Existing ArgumentError ~~~ def test yield 1 end test(&plus) # Would raise ArgumentError 1 for 2 ~~~ What would happen in the case where you don't convert the lambda to a block and call with an array of the same length as the lambda's arity? ~~~ def test l l.call [1,2] end test(plus) ~~~ Currently it raises "ArgumentError: wrong number of arguments (1 for 2)". It feels a bit strange to me if that behavior continues but is different the similar example with an array and lambda converted to a block. ---------------------------------------- Bug #9605: Chaining "each_with_index.detect &lambda" raises ArgumentError https://bugs.ruby-lang.org/issues/9605#change-45762 * Author: Alex Rothenberg * Status: Rejected * Priority: Normal * Assignee: * Category: * Target version: * ruby -v: 2.1.1 * Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN ---------------------------------------- I found an odd edge case where "detect" and "select" behave differently from other methods of Enumerable. Normally these methods yield a single argument to a block but when you chain them after "each_with_index" they yield two arguments "item" and "index". The problem is when you try passing a lambda instead of a block then they raise an ArgumentError $ irb 2.1.1 :001 > lambda = ->(word, index) { word.length == 3 } => # 2.1.1 :002 > %w(Hi there how are you).each_with_index.detect &lambda ArgumentError: wrong number of arguments (1 for 2) from (irb):1:in `block in irb_binding' from (irb):2:in `each' from (irb):2:in `each_with_index' from (irb):2:in `each' from (irb):2:in `detect' from (irb):2 from /Users/alex/.rvm/rubies/ruby-2.1.1/bin/irb:11:in `
' 2.1.1 :003 > %w(Hi there how are you).each_with_index.select &lambda ArgumentError: wrong number of arguments (1 for 2) from (irb):1:in `block in irb_binding' from (irb):3:in `each' from (irb):3:in `each_with_index' from (irb):3:in `each' from (irb):3:in `select' from (irb):3 from /Users/alex/.rvm/rubies/ruby-2.1.1/bin/irb:11:in `
' Interestingly it works just find when calling other methods like "map" 2.1.1 :004 > %w(Hi there how are you).each_with_index.map &lambda => [false, false, true, true, true] It also works when you use a proc 2.1.1 :001 > proc = Proc.new {|word, index| word.length == 3 } => # 2.1.1 :002 > %w(Hi there how are you).each_with_index.detect &proc => ["how", 2] 2.1.1 :003 > %w(Hi there how are you).each_with_index.map &proc => [false, false, true, true, true] or a block 2.1.1 :001 > %w(Hi there how are you).each_with_index.detect {|word, index| word.length == 3 } => ["how", 2] 2.1.1 :002 > %w(Hi there how are you).each_with_index.map {|word, index| word.length == 3 } => [false, false, true, true, true] When testing against JRuby or Rubinius none of these scenarios raise an ArgumentError. I'm guessing this is a bug and not intended behavior. If it is intended then both those implementations have a bug in not raising ArgumentError. -- http://bugs.ruby-lang.org/