From: jakesower@...
Date: 2014-12-31T20:43:55+00:00
Subject: [ruby-core:67259] [ruby-trunk - Bug #10684] Block arity changes through Enumerable methods

Issue #10684 has been updated by Jake Sower.


Blocks traveling through methods in Enumerable have their arity changed before reaching #each. Example:

```ruby
class MyEnumerable
  include Enumerable

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

my_enum = MyEnumerable.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.

----------------------------------------
Bug #10684: Block arity changes through Enumerable methods
https://bugs.ruby-lang.org/issues/10684#change-50726

* 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
----------------------------------------
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.



-- 
https://bugs.ruby-lang.org/