Feature #21678: Enumerable#rfind

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

[kddnewton (Kevin Newton)]

I'd like to introduce rfind to enumerable, which would effectively be the same as reverse_each.find. I've found myself using this a surprising number of times, and have been surprised at its omission. That means either falling back to reverse_each or rindex.

For context, here are a couple of examples of this in the wild:

• pry
• bundler
• textbringer

[nobu (Nobuyoshi Nakada)]

https://github.com/nobu/ruby/tree/refs/heads/enum-rfind

[matz (Yukihiro Matsumoto)]

The Enumerable module basically relies on the #each method which only works in the forward direction, and the only way to scan backwards is to convert it to an array once. I agree with Array#rfind (which can be implemented efficiently), but is it necessary for the Enumerable module as well?

Matz.

[kddnewton (Kevin Newton)]

That makes sense! I'm totally fine with it just being on Array.

[kddnewton (Kevin Newton)]

https://github.com/ruby/ruby/pull/15189

[kddnewton (Kevin Newton)]

• Status changed from Open to Closed

Applied in changeset git|6147b695870ce82ee3ad5305ce095b63889b8d9d.

---

Array#rfind

Implement Array#rfind, which is the same as find except from the
other side of the Array. Also implemented Array#find (as opposed to
the generic one on Enumerable because it is significantly faster
and to keep the implementations together.

[Feature #21678]

[etienne (Étienne Barrié)]

Should we alias detect to also use that Array-specific faster implementation?

>> [].method :detect
=> #<Method: Array(Enumerable)#detect(*)>
>> [].method :find
=> #<Method: Array#find(*)>

Edit: https://github.com/ruby/ruby/pull/15558

[Eregon (Benoit Daloze)]

@etienne Yes, that seems clearly a good fix, could you do it?
(I personally don't like detect but we should keep aliases consistent in performance and behavior)

[kddnewton (Kevin Newton)]

Is this an issue where you could have defined Enumerable#find and now it won't have overwritten Array#find? Should I revert that part of this patch?