From: Bug Free <amberarrow@...>
Date: 2011-11-23T12:12:48+09:00
Subject: block.arity when using each_with_index

Hi,

I have a class with a custom iterator (each) that uses block.arity to
determine how many arguments to use on the yield. It works well but
when the caller invokes the iterator via each_with_index, the value
of block.arity is -1 which wreaks havoc. Does anyone know how to get the
correct value of block.arity in this situation?\

ruby -v
ruby 1.9.3p0 (2011-10-30) [x86_64-linux]

Here is the sample code:
-------------------------------------------

#!/usr/bin/ruby -w

# test block.arity value with each_with_index

class A
  include Enumerable

  def each( p, &b )
    puts "arity = #{b.arity}"
    yield 'hello', 'world'
  end
end

a = A.new
a.each( 0 ) { |x, y| puts "x = #{x}, y = #{y}" }
a.each_with_index( 0 ) { |(x, y), i| puts "x = #{x}, y = #{y}" }
----------------------------------------------------------------

Here is the output:

arity = 2
x = hello, y = world
arity = -1
x = hello, y = world

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