From 24db1f29fe930df680b6f79503f463ebb01e044e Mon Sep 17 00:00:00 2001
From: Marina Glancy <marina@moodle.com>
Date: Mon, 20 Dec 2021 17:07:05 +0100
Subject: [PATCH] MDL-73420 core: make static cache compatible with PHP8.1

---
 lib/classes/persistent.php | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/classes/persistent.php b/lib/classes/persistent.php
index d9ec2bde40e..de9419c72ae 100644
--- a/lib/classes/persistent.php
+++ b/lib/classes/persistent.php
@@ -274,12 +274,13 @@ abstract class persistent {
     final public static function properties_definition() {
         global $CFG;
 
-        static $def = null;
-        if ($def !== null) {
-            return $def;
+        static $cachedef = [];
+        if (isset($cachedef[static::class])) {
+            return $cachedef[static::class];
         }
 
-        $def = static::define_properties();
+        $cachedef[static::class] = static::define_properties();
+        $def = &$cachedef[static::class];
         $def['id'] = array(
             'default' => 0,
             'type' => PARAM_INT,