Bug #19569
closed#map on Enumerator::Lazy block arguments seem to differ from regular #map
Description
A Ruby 2 to 3 upgrade surfaced the following issue:
Ruby 2:
irb(main):252:0> [1, 2, 3].to_enum.lazy.zip([:a, :b, :c]).map(&:last).to_a
=> [:a, :b, :c]
Ruby 3:
irb(main):020:0> [1, 2, 3].to_enum.lazy.zip([:a, :b, :c]).map(&:last).to_a
(irb):20:in `each': undefined method `last' for 1:Integer (NoMethodError)
Debugging the issue, I noticed the following:
Map with a block returns only the first argument (and seems to ignore the zipped list):
irb(main):024:0> [1, 2, 3].to_enum.lazy.zip([:a, :b, :c]).map { |x| x }.to_a
=> [1, 2, 3]
It's not actually ignored though, it's just passed as a second argument:
irb(main):025:0> [1, 2, 3].to_enum.lazy.zip([:a, :b, :c]).map { |*x| x }.to_a
=> [[1, :a], [2, :b], [3, :c]]
Thus, this looks like a workaround:
irb(main):026:0> [1, 2, 3].to_enum.lazy.zip([:a, :b, :c]).map { |*x| x.last }.to_a
=> [:a, :b, :c]
But it behaves differently when leaving the lazy
out:
irb(main):027:0> [1, 2, 3].to_enum.zip([:a, :b, :c]).map { |*x| x.last }.to_a
=> [[1, :a], [2, :b], [3, :c]]
Not sure if I'm correct in my conclusion, but to me it looks like the argument handling of map
and lazy_map
differs in an unexpected manner. Is this a bug/oversight, or I am simply using the different map implementations wrong?
Updated by TomNaessens (Tom Naessens) 8 months ago
- Subject changed from #map on Enumerator::Lazy block arguments differ from regular #map to #map on Enumerator::Lazy block arguments seem to differ from regular #map
Updated by jeremyevans0 (Jeremy Evans) 5 months ago
This is because Enumerator::Lazy#zip marks the enumerator as packed when it shouldn't (introduced with the optimization in 54acb3dd52a5fe75c32c3e36a6984d3ec4314a72). I've submitted a pull request to fix this: https://github.com/ruby/ruby/pull/7967
Updated by jeremyevans (Jeremy Evans) 5 months ago
- Status changed from Open to Closed
Applied in changeset git|a14915ca4baae40f08d288a38b8bfb595500ad90.
Do not have Enumeratory::Lazy#zip mark result as packed
Fixes [Bug #19569]