From: "Strech (Sergey Fedorov) via ruby-core" <ruby-core@...>
Date: 2026-06-26T14:54:30+00:00
Subject: [ruby-core:125843] [Ruby Bug#22131] Avoid array allocation in `Array#include?` on literal arrays

Issue #22131 has been updated by Strech (Sergey Fedorov).


nobu (Nobuyoshi Nakada) wrote in #note-1:
> Also `putnil` could be optimized.

Yes, I thought about it, but decide to start small, I'm going to add it

----------------------------------------
Bug #22131: Avoid array allocation in `Array#include?` on literal arrays
https://bugs.ruby-lang.org/issues/22131#change-117762

* Author: Strech (Sergey Fedorov)
* Status: Open
* ruby -v: ruby 4.1.0dev
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
I've noticed that `Array#include?` on a literal array of frozen-shareable elements (Integers, Symbols, true/false/nil, frozen String literals) compiles the receiver to `duparray`, which allocates a fresh `Array` copy on every call ��� even though `#include?` only reads it.


**Before**

```ruby
# frozen_string_literal: true
[1, 2].include?(3)
```

```                        
== disasm: #<ISeq:<main>@-e:2 (2,0)-(2,18)>
0000 duparray                               [1, 2]                    (   2)[Li]
0002 putobject                              3
0004 opt_send_without_block                 <calldata!mid:include?, argc:1, ARGS_SIMPLE>
0006 leave
```

**After**

```ruby
# frozen_string_literal: true
[1, 2].include?(3)
```

```
== disasm: #<ISeq:<main>@-e:2 (2,0)-(2,18)>
0000 putobject                              3                         (   2)[Li]
0002 opt_duparray_send                      [1, 2], :include?, 1
0006 leave
```

**Benchmarks**


```ruby
require 'benchmark/ips'

GC.disable

ARR = [1, 2, 3]

Benchmark.ips do |x|
  x.report "literal  [1,2,3].include?(2)" do |loop|
    loop.times { [1, 2, 3].include?(2) }
  end
  x.report "constant ARR.include?(2)" do |loop|
    loop.times { ARR.include?(2) }
  end
  x.compare!
end
```

| case | master | candidate | speedup |
|---|---|---|---:|
| `[1,2,3].include?(2)` | 17.83M i/s (56.09 ns) | 30.00M i/s (33.33 ns) | 1.68x |
| `ARR.include?(2)` (const) | 23.92M i/s (41.80 ns) | 23.92M i/s (41.81 ns) | ~1.00x |

Github PR: https://github.com/ruby/ruby/pull/17496



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