From: "ioquatix (Samuel Williams) via ruby-core" <ruby-core@...>
Date: 2024-01-14T00:31:05+00:00
Subject: [ruby-core:116192] [Ruby master Feature#20182] Rewrite Array#each in Ruby

Issue #20182 has been updated by ioquatix (Samuel Williams).


I think this is a great idea and would like to see. more of Ruby implemented in Ruby. The smaller the C implementation becomes, the better.

----------------------------------------
Feature #20182: Rewrite Array#each in Ruby
https://bugs.ruby-lang.org/issues/20182#change-106206

* Author: k0kubun (Takashi Kokubun)
* Status: Open
* Priority: Normal
----------------------------------------
## Proposal

Rewrite Array#each in Ruby https://github.com/ruby/ruby/pull/6687.

```rb
class Array
  def each
    unless block_given?
      return to_enum(:each) { self.length }
    end
    i = 0
    while i < self.length
      yield self[i]
      i = i.succ
    end
    self
  end
end
```

## Purpose

Make it possible for YJIT to optimize ISEQs across `Array#each`.

## Background

Whether JIT-compiled or not, calling Ruby from C is more expensive than calling Ruby from Ruby. It also prevents YJIT from making cross-ISEQ optimizations.

This is problematic especially for loop methods written in C like `Array#each` since the overhead is repeated at every iteration.

## Discussions

There are a couple of things I'd like to discuss in this ticket:

1. @Eregon has pointed out that there's a race condition in the above implementation. `self[i]` would yield `nil` if the element was removed by another thread or TracePoint after `i < self.length`. Is it `Array#each`'s responsibility to atomically operate on elements, or are users supposed to avoid mutating the array in the middle of its loop?
2. If `Integer#<`, `Integer#length`, `Integer#succ`, or `Array#[]` is overridden in an incompatible way, the Ruby implementation may not work correctly. May I assume it's acceptable?



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