error global

INDUK KELAS DATABASE (Sebagai Parent Kelas)
<?php

	class Kelas_database{
		var $hostname = "localhost";
		var $username = "root";
		var $password = "";
		var $database = "keuangan";

		public function __construct(){

			$link = mysqli_connect($this->hostname, $this->username, $this->password, $this->database) or die('gagal konek');


			// if ($link) {
			// 	# code...
			// 	echo "Koneksi database mysqli berhasil konek";
			// }else{
			// 	echo "koneksi database mysqli gagal konek";
			// }
		}
	}

 ?>

#==================================================================================================================
Kelas Log-in
(Kelas Login ikut ke induk database)

<?php

	include 'config/kelas_database.php';

	class kelas_login extends kelas_database{

		public function method_login($email_user, $password){
			global $link;

			$query = "SELECT * FROM tbl_user WHERE email_user = '$email_user' AND password = '$password'";
			$result = mysqli_query($link, $query) or die('tidak dapat akses database, login gagal');

			return $result;
		}
	}

 ?>
#==================================================================================================================
index.php
Untuk proses form login

<?php

    # panggil file login
    include 'function/kelas_login.php';

    # Panggil kelas login
    $kelas_login = new kelas_login();

    @$email_user = $_POST['txtEmail'];
    @$password  = $_POST['txtPassword'];

    # Panggil method login
    echo $kelas_login->method_login($email_user, $password);
 ?>