[ruby-core:113476] [Ruby master Feature#19294] Enumerator.product works incorrectly with consuming enumerators

Issue #19294 has been updated by jeremyevans0 (Jeremy Evans).

Backport deleted (2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: UNKNOWN)
Tracker changed from Bug to Feature

@headius and I discussed this.  We don't think it is possible to get the output requested without keeping all enumerated elements for arguments after the first argument in memory, which is not acceptable by default.  It's possible that behavior could be considered via a keyword argument, but that would be a feature request and not a bug fix.

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Feature #19294: Enumerator.product works incorrectly with consuming enumerators
https://bugs.ruby-lang.org/issues/19294#change-103058

* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
----------------------------------------
```ruby
s = StringIO.new('abc')
Enumerator.product([1, 2, 3], s.each_char).to_a
# Expected: => [[1, "a"], [1, "b"], [1, "c"], [2, "a"], [2, "b"], [2, "c"], [3, "a"], [3, "b"], [3, "c"]]
# Actual: => [[1, "a"], [1, "b"], [1, "c"]]
```
The implementation consumes the non-first enumerator to produce the first combination.

Somewhat related to the dilemma of consuming and non-consuming enumerators (#19061).

PS: I noticed I don't understand why it is `Enumerator.product` and not `Enumerable#product`, but probably it is too late to raise the questions :(



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