参见英文答案 > Predefined types of variable parameters4个
我在 https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Console/Output/Output.php第40行看到了这个代码,他们正在使用？int.

public function __construct(?int $verbosITy = self::VERBOSITY_NORMAL,bool $decorated = false,OutputFormatterInterface $formatter = null)
    {
        $this->verbosity = null === $verbosity ? self::VERBOSITY_NORMAL : $verbosity;
        $this->formatter = $formatter ?: new OutputFormatter();
        $this->formatter->setDecorated($decorated);
    }

function nullOrInt(?int $arg){
    var_dump($arg);
}

nullOrInt(100);
nullOrInt(null);