Get type of typed property in PHP 7.4

I have a DTO with typed PHP variables:

class CreateMembershipInputDto extends BaseDto
{
    public bool $is_gift;
    public int $year;
    public string $name;
    public \DateTime $shipping_date;
    public ContactInputDto $buyer;
    public ?ContactInputDto $receiver;
}

I am trying to make some kind of automapper, which fills the properties, but I need to check the type of the variable but that seems to be impossible.

class BaseDto
{
    public function __construct($json)
    {
        $jsonArray = json_decode($json, true);
        foreach($jsonArray as $key=>$value){
            $type = gettype($this->$key);
            if($type instanceof BaseDto)
                $this->$key = new $type($value);
            else
                $this->$key = $value;
        }
    }
}

ContactInputDto:

class ContactInputDto extends BaseDto
{
    public string $firstname;
    public string $lastname;
    public string $street_housenumber;
    public string $postal_code;
    public string $place;
    public string $country;
    public string $email;
    public string $phone;
}

Is it somehow possible to make that line "gettype($this->$key)" work, without php throwing the following error:

Typed property App\Dto\CreateMembershipInputDto::$is_gift must not be accessed before initialization

While the manual does not seem to currently document it, there is a method added to ReflectionProperty to allow you to get the type. This is actually specified in the RFC for typed properties

Here's how you would use it:

class CreateMembershipInputDto extends BaseDto {
    public bool $is_gift;
    public int $year;
    public string $name;
    public \DateTime $shipping_date;
    public ContactInputDto $buyer;
    public ?ContactInputDto $receiver;
}

class BaseDto
{
    public function __construct($json)
    {   
        $r = new \ReflectionClass(static::class); //Static should resolve the the actual class being constructed
        $jsonArray = json_decode($json, true);
        foreach($jsonArray as $key=>$value){
            $prop = $r->getProperty($key);
            if (!$prop || !$prop->getType()) { continue; } // Not a valid property or property has no type   
            $type = $prop->getType();
            if($type->getName() === BaseDto::class) //types names are strings
                $this->$key = new $type($value);
            else
                $this->$key = $value;
        }
    }
}

If you want to check if the type extends BaseDto you will need (new \ReflectionClass($type->getName()))->isSubclassOf(BaseDto::class)

Note that getName refers to to ReflectionNamedType::getName. Prior to PHP 8 this was the only possible instance you could get $prop->getType() however starting PHP 8 you may also get a ReflectionUnionType which contains multiple types