Issue #13648 has been reported by akihikodaki (Akihiko Odaki).

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Bug #13648: [PATCH] Nested map of Enumerator::Lazy with packed values gives wrong result
https://bugs.ruby-lang.org/issues/13648

* Author: akihikodaki (Akihiko Odaki)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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This test case ends up with the following result.

~~~ ruby
class Step
  include Enumerable
  attr_reader :current, :args

  def initialize(enum)
    @enum = enum
    @current = nil
    @args = nil
  end

  def each(*args)
    @args = args
    @enum.each do |v|
      @current = v
    if v.is_a? Enumerable
      yield *v
    else
      yield v
    end
  end
end

a = Step.new([[1, 2]])
assert_equal([[[1, 2]]], a.lazy.map {|*args| args}.map {|*args| args}.to_a)
~~~

~~~
<[[[1, 2]]]> expected but was
<[[1, 2]]>.
~~~

Here, `[[[1, 2]]]` is expected because:
* An array should be created with the first map, which results in `[1, 2]`.
* The array should be wrapped in another array with the second map, which results in `[[1, 2]]`.
* The array should be wrapped in another array with to_a, which results in `[[[1, 2]]]`.

However, it returns `[[1, 2]]` because:
* An array will be created with the first map, which results in `[1, 2]`.
* However, the array will be internally considered as "packed" and the unpacked arguments will be passed to the second map.
* The second map wraps them into another array, which results in `[1, 2]`.
* The array will be wrapped in another array with to_a, which results in `[[1, 2]]`.

I have attached the test case and a fix. The fix marks values returned by blocks are not packed.

---Files--------------------------------
fix.patch (2.18 KB)


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