Issue #19569 has been reported by TomNaessens (Tom Naessens). ---------------------------------------- Bug #19569: #map on Enumerator::Lazy block arguments differ from regular #map https://bugs.ruby-lang.org/issues/19569 * Author: TomNaessens (Tom Naessens) * Status: Open * Priority: Normal * ruby -v: 3.0.5...3.2.0 * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- 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? -- https://bugs.ruby-lang.org/