如何为构造函数指定返回类型

For consistency I'm specifying return types since PHP 7.1, for all methods, including magic ones like __toString, and even when the implicit return type is void like with __unserialize():

class a {
  function __toString() : string {}
  function __unserialize ( array $data ) : void {}
}

当我尝试使用相同的构造函数和析构函数时,如下所示:

class a {
  function __construct() : void {}
  function __destruct() : void {}
}

PHP yields Fatal errors:

Constructor a::__construct() cannot declare a return type
Destructor a::__destruct() cannot declare a return type

我现在唯一能做的就是在像这样的docblock中指定隐式返回类型:

/**
 * @return void (implicit)
 */

It puzzles me why, because other predefined methods do support an explicit return type. I couldn't find anything about this deviation in the docs, or in the RFC.

如何为构造函数和析构函数指定返回类型?如果在PHP 7中不可能,在PHP 8中是否有可能?