Feature #18551
closedMake `Range#reverse_each` to raise an exception if endless
Description
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>'
Updated by Eregon (Benoit Daloze) almost 3 years ago
There is no Range#reverse_each currently, only Enumerable#reverse_each, and Enumerable can't know about this.
But maybe it makes sense to have Range#reverse_each for this and maybe also for faster reverse_each on Numeric Ranges?
OTOH Range operations that work differently for numerics tend to make Range even more messy when it comes to non-numeric values (more differences in behavior, can't reverse_each
efficiently on Date/Time/etc).
Updated by Eregon (Benoit Daloze) almost 3 years ago
I checked the PR, seems a useful change to me.
Updated by Dan0042 (Daniel DeLorme) almost 3 years ago
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...
Updated by kyanagi (Kouhei Yanagita) almost 3 years ago
Eregon (Benoit Daloze) wrote in #note-1:
OTOH Range operations that work differently for numerics tend to make Range even more messy when it comes to non-numeric values (more differences in behavior, can't
reverse_each
efficiently on Date/Time/etc).
I posted another ticket for performance issue: #18515
I wrote my thoughts there.
Updated by nobu (Nobuyoshi Nakada) 12 months ago
- Subject changed from Make Range#reverse_each to raise an exception if endless to Make `Range#reverse_each` to raise an exception if endless
Updated by mame (Yusuke Endoh) 11 months ago
In the previous dev meething, matz accepted this. I will merge the PR
Updated by kyanagi (Kouhei Yanagita) 11 months ago
- Status changed from Open to Closed
Applied in changeset git|458d079166ce7344c1d44b2403ff963b8c68d7d8.
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