关于 laravel 中array_set的疑问

/**
	 * Set an array item to a given value using "dot" notation.
	 *
	 * If no key is given to the method, the entire array will be replaced.
	 *
	 * @param  array   $array
	 * @param  string  $key
	 * @param  mixed   $value
	 * @return array
	 */
	public static function set(&$array, $key, $value)
	{
		if (is_null($key)) return $array = $value;
		$keys = explode('.', $key);
		while (count($keys) > 1)
		{
			$key = array_shift($keys);
			// If the key doesn't exist at this depth, we will just create an empty array
			// to hold the next value, allowing us to create the arrays to hold final
			// values at the correct depth. Then we'll keep digging into the array.
			if ( ! isset($array[$key]) || ! is_array($array[$key]))
			{
				$array[$key] = array();
			}
			$array =& $array[$key];//这里吧$array 覆盖到 $array 
		}
		$array[array_shift($keys)] = $value;
		return $array;//这里最终返回的成你操作的最后一个层级了，
//不在是原数组了啊，如果你操作的是顶层的不会看到
//这个BUG如果是二次 三层 返回的永远是最后一层啊
	}