[ruby-core:113976] [Ruby master Bug#19569] #map on Enumerator::Lazy block arguments seem to differ from regular #map
From:
"jeremyevans0 (Jeremy Evans) via ruby-core" <ruby-core@...>
Date:
2023-06-21 17:26:58 UTC
List:
ruby-core #113976
Issue #19569 has been updated by jeremyevans0 (Jeremy Evans).
This is because Enumerator::Lazy#zip marks the enumerator as packed when it shouldn't (introduced with the optimization in commit:54acb3dd52a5fe75c32c3e36a6984d3ec4314a72). I've submitted a pull request to fix this: https://github.com/ruby/ruby/pull/7967
----------------------------------------
Bug #19569: #map on Enumerator::Lazy block arguments seem to differ from regular #map
https://bugs.ruby-lang.org/issues/19569#change-103634
* 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/
______________________________________________
ruby-core mailing list -- ruby-core@ml.ruby-lang.org
To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
ruby-core info -- https://ml.ruby-lang.org/mailman3/postorius/lists/ruby-core.ml.ruby-lang.org/