[ruby-core:67258] [ruby-trunk - Bug #10684] [Open] Block arity changes through Enumerable methods

Issue #10684 has been reported by Jake Sower.

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Bug #10684: Block arity changes through Enumerable methods
https://bugs.ruby-lang.org/issues/10684

* Author: Jake Sower
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: 2.2.0
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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Blocks traveling through methods in Enumerable have their arity changed before reaching #each.  Example:


class MyEnumerator
  include Enumerable

  def initialize(ary)
    @ary = ary
  end

  def each(&block)
    puts block.arity
    @ary.each(&block)
  end
end

my_enum = MyEnumerator.new([1,2,3])
my_enum.each{|x| x}    # outputs 1
my_enum.detect{|x| x}  # outputs -1



This is surprising behavior.  I would expect the output to be 1 in both cases since the blocks appear identical to me as a programmer.



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