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#to_ary behavior does not conform to MRI behavior #3377

asthasr opened this Issue Oct 8, 2015 · 2 comments


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commented Oct 8, 2015

In MRI Ruby, when you iterate over an object providing a block with extra parameters, it seems that #to_ary is called and, if it returns nil, is disregarded. This is a test that you can execute to see the behavior on different Rubies:

class Example
  def to_ary

test = [].map { |x, _| x }

puts test == [nil] ? "fail" : "pass"

On MRI versions, this passes. On JRuby 1.7.22, it returns [nil] and thus fails. On JRuby, it raises an exception: TypeError: Example#to_ary should return Array. It seems that the behavior in this case should conform to the behavior on MRI, in order to avoid surprising behavior when attempting to use map, each and other enumerable methods.

In real projects, this is observable on any ActiveRecord object as well as DelayedJob, as seen in Issue #3338.


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commented Oct 8, 2015

Ahh phooey...just when I think we've got to_ary working exactly right, some other case comes up. Will investigate.


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commented Oct 8, 2015

I will fix this as part of 1.7.x but the fix for this was done earlier in a commit I noted in #3338.

@enebo enebo added this to the JRuby 1.7.23 milestone Oct 8, 2015

enebo added a commit that referenced this issue Oct 8, 2015

@enebo enebo closed this Oct 8, 2015

@kares kares added the JRuby 1.7.x label Nov 15, 2015

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