返回数据库对象的PHP方法的返回类型？

Question

What return type I should replace in "WHAT?" text. And if the query returns no results?

I'm using PHP 7.1

The method is:

public function retrieveSomething(int $id_user): WHAT? {
    try {
        $this->sql = 'SELECT * FROM tbl_users WHERE IdUser = :id_user';
        $stmt = $this->db->prepare($this->sql);
        $stmt->bindValue(':id_user', $id_user, PDO::PARAM_INT);
        $stmt->execute();
        $row = $stmt->fetch(PDO::FETCH_OBJ);
        $stmt->closeCursor();
        return $row;
    } catch (PDOException $e) {
        throw $e;
    } catch (Exception $e) {
        throw $e;
    }
}

Answer 1

From manual:

PDO::FETCH_OBJ: returns an anonymous object with property names that correspond to the column names returned in your result set

You have some examples among the user comments:

object(stdClass)#6 (3) {
  ["1"]=>
  string(1) "1"
  ["2"]=>
  string(1) "2"
  ["3"]=>
  string(1) "3"
}

So:

public function retrieveSomething(int $id_user): \stdClass {
}

... should work (I don't have PHP/7 here to test).

Also:

The return value of this function on success depends on the fetch type. In all cases, FALSE is returned on failure.

To avoid this, you should configure PDO to throw exceptions (which you apparently already did, and is a good idea by itself).

Additionally, I suggest you drop the try/catch blocks, they're completely redundant.