https://git.ruby-lang.org/ruby.git/commit/?id=e1e61e256b

From e1e61e256bd65ac3f293ba1513d1a934b9a3bff9 Mon Sep 17 00:00:00 2001
From: Masaki Matsushita <glass.saga@g...>
Date: Sat, 6 Feb 2021 17:01:42 +0900
Subject: Improve performance of Array#- when it is called with empty array

This change make Array#- return a copy of the receiver when
the other array is empty.
---
 array.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/array.c b/array.c
index a73f418..ad7e11a 100644
--- a/array.c
+++ b/array.c
@@ -5291,6 +5291,7 @@ rb_ary_diff(VALUE ary1, VALUE ary2) https://github.com/ruby/ruby/blob/trunk/array.c#L5291
     long i;
 
     ary2 = to_ary(ary2);
+    if (RARRAY_LEN(ary2) == 0) { return ary_make_shared_copy(ary1); }
     ary3 = rb_ary_new();
 
     if (RARRAY_LEN(ary1) <= SMALL_ARRAY_LEN || RARRAY_LEN(ary2) <= SMALL_ARRAY_LEN) {
-- 
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