Issue #16414 has been updated by jeremyevans0 (Jeremy Evans).


I have a possible fix for this: https://github.com/ruby/ruby/pull/2742

After CI completes, I'll try to merge it so it makes 2.7.0-rc1.

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Bug #16414: Incompatible behavior of Proc/lambda with single argument when using `Enumerator::Lazy#with_index`
https://bugs.ruby-lang.org/issues/16414#change-83075

* Author: tomog105 (Tomohiro Ogoke)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.7.0dev (2019-12-10T10:12:21Z master af11efd377) [x86_64-darwin18]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
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The following code raised an error `wrong number of arguments (given 1, expected 2) (ArgumentError)` in master.

```
$ ruby -e 'lambda = -> (s, i) { "#{i}:#{s}" }; p %w(a b c).each.lazy.with_index.map(&lambda).first(2)'
# expected result => ["0:a", "1:b"]
```

This code is valid up till Ruby 2.6.5 and 2.7.0-preview1, but it raised the error in Ruby 2.7.0-preview2 or later. Maybe, this behavior has been there since the implementation of `Enumerator::Lazy#with_index`.

Is this behaviour intended?



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