[ruby-core:107326] [Ruby master Feature#18551] Make Range#reverse_each to raise an exception if endless

Issue #18551 has been updated by Dan0042 (Daniel DeLorme).


Yes, this is a useful change. Although wouldn't it be better to prevent `#to_a` instead of only `#reverse_each` ?

Actually there's quite a lot of Enumerable methods that would be better raising an exception for endless ranges.
For example: `(1..).select{ true }` results in infinite loop and memory consumption.
The only way out is `break`, but then there's no point using `select` since it can't return a result.
The same applies to reject, partition, sort, zip, uniq, tally, etc...

----------------------------------------
Feature #18551: Make Range#reverse_each to raise an exception if endless
https://bugs.ruby-lang.org/issues/18551#change-96224

* Author: kyanagi (Kouhei Yanagita)
* Status: Open
* Priority: Normal
----------------------------------------
https://github.com/ruby/ruby/pull/5498

Currently, `Range#reverse_each` for an endless range never returns.

```
% ruby -e '(1..).reverse_each { }'
# never return ...
```

(This is because `Enumerable#reverse_each` tries `#to_a` and `#to_a` for an endless range comes into an infinite loop.)

I think `Range#reverse_each` for an endless range should raise an exception, similar to `Range#each` for a beginless range.

```
% ruby -e '(..1).each { }' 
-e:1:in `each': can't iterate from NilClass (TypeError)
	from -e:1:in `<main>'
```




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