[PHP]Wywołanie klasy w konstruktorze Opcje

[-etup-]

Dlaczego ten kod wyświetla taki komunikat:

Catchable fatal error: Argument 1 passed to Theme::__construct() must be an instance of Config, none given, called in /var/www/index.php on line 8 and defined in /var/www/theme.php on line 7

index.php

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include_once 'config.php';
include_once 'theme.php';
 
$test = new Theme;
echo $test-> show();
[PHP] pobierz, plaintext 

theme.php

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class Theme
{
    private $db;
 
    public function __construct(Config $db)
    {
        $this->db = $db;
    }
 
    public function show()
    {
        return $this->db;
    }
}
[PHP] pobierz, plaintext 

config.php

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class Config
{
    public $host;
    private $user;
    private $pswd;
    private $baza;
 
 
    public function __construct()
    {
        $this->host = 'host';
        $this->user = 'user';
        $this->pswd = 'password';
        $this->baza = 'baza';
    }
 
}
[PHP] pobierz, plaintext 

Jak to naprawić?