Feature #17347: Enumerator::Chain of Enumerator::Lazy should be lazy

• Status: Closed
• Assignee: -
• Target version: -

[asilano (Chris Howlett)]

ruby 2.6.6p146 (2020-03-31 revision 67876) [x86_64-linux]

Consider the following script:

a = [1,2,3].lazy
p a
b = [4,5,6].lazy
p b
c = a + b
p c

This gives the output:

#<Enumerator::Lazy: [1, 2, 3]>
#<Enumerator::Lazy: [4, 5, 6]>
#<Enumerator::Chain: [#<Enumerator::Lazy: [1, 2, 3]>, #<Enumerator::Lazy: [4, 5, 6]>]>

Note that c is just Enumerator::Chain; but all its component enumerators are lazy, so it would be nice if c were lazy.

That is, I'd like the output to be:

#<Enumerator::Lazy: [1, 2, 3]>
#<Enumerator::Lazy: [4, 5, 6]>
#<Enumerator::Lazy: #<Enumerator::Chain: [#<Enumerator::Lazy: [1, 2, 3]>, #<Enumerator::Lazy: [4, 5, 6]>]>>

[nobu (Nobuyoshi Nakada)]

• Is duplicate of Bug #17216: Enumerator::Chain doesn't support all Enumerator methods added

[asilano (Chris Howlett)]

Is it a duplicate? I can see it's similar, but I'm not entirely sure fixing #17216 will fix this. Willing to be wrong, though.

[jeremyevans0 (Jeremy Evans)]

This isn't a duplicate of #17216 even though it is related. I agree that this feature would be useful. I've included an implementation in the same pull request: https://github.com/ruby/ruby/pull/3811

• Status changed from Open to Closed

Applied in changeset git|bf40fe9fed19a5e22081b133661c0629988f1618.

---

Fix calling enumerator methods such as with_index on Enumerator::Chain

This previously raised a TypeError. Wrap the Enumerator::Chain in
an Enumerator to work around the problem.

Fixes [Bug #17216]