pocketmine\level\GameRules::setOrCreateGameRule PHP Method

    public function setOrCreateGameRule($key, $ruleValue)
    {
        // print("setting " . $key . " to " . $ruleValue . "\n");
        $value = $this->theGameRules[$key];
        if ($value != null) {
            $this->theGameRules[$key] = $ruleValue;
        } else {
            $this->addGameRule($key, $ruleValue, Tag::class);
        }
    }

 public function setGameRule($name, $value)
 {
     $this->gamerules->setOrCreateGameRule($name, $value);
     return $this->gamerules->hasRule($name);
 }