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Bug #9605

closed

Chaining "each_with_index.detect &lambda" raises ArgumentError

Added by alexrothenberg (Alex Rothenberg) over 7 years ago. Updated almost 7 years ago.

Status:
Closed
Priority:
Normal
Target version:
[ruby-core:61340]

Description

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 }
=> #<Proc:0x007ff8848630d8@(irb):1 (lambda)>
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 `<main>'

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 `<main>'

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 }
=> #<Proc:0x007fc375a3a558@(irb):1>
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.

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