组合方式实现多重继承（表象模拟）
---采用的是类内部实现对象引用技术

class Student
{
    private $name = '袭人';
    public function getName() {
        echo $this->name . "\n";
    }
}

class Teacher
{
    private $work_year = 3;
    public function getWorkYear() {
        echo $this->work_year . "\n";
    }
}

class GraduateStudent extends Student
{
    private $teacher;

    public function __construct()
    {
        $this->teacher = new Teacher();
    }

    public function getWorkYear()
    {
        $this->teacher->getWorkYear();
    }

}

$BaoChai = new GraduateStudent();
$BaoChai->getWorkYear();

接口方式实现多重继承（完全模拟）
---通过把类的特征抽象为接口，并通过实现接口的方式让对象有多重身份。

interface User
{
    function getName();
}

interface Teacher
{
    function getWorkYear();
}

class Student implements User
{
    private $name = '晴雯';

    public function getName()
    {
        echo "Student name is $this->name <br>";
    }
}

/*class GraduateTeacher implements Teacher
{
    private $work_year = 3;

    public function getWorkYear()
    {
        echo "Teacher work year is $this->work_year <br>";
    }
}*/

class GraduateStudent extends Student implements Teacher
{
    /*private $teacher;

    public function __construct()
    {
        $this->teacher = new GraduateTeacher();
    }

    public function getWorkYear()
    {
        $this->teacher->getWorkYear();
    }
    */

    private $work_year = 3;

    public function getWorkYear()
    {
        echo "Teacher work year is $this->work_year <br>";
    }


}

$BaoChai = new GraduateStudent();
$BaoChai->getName();
$BaoChai->getWorkYear();


class Test
{
     //User是接口名
    static function getName(User $student) {
        $student->getName();
    }

    //Teacher是接口名
    static function getWorkYear(Teacher $teacher) {
        $teacher->getWorkYear();
    }
}

echo '<hr>';

Test::getName($BaoChai);
Test::getWorkYear($BaoChai);

/*
 * 结果：
Student name is 晴雯 
Teacher work year is 3 
-------------------------------------
Student name is 晴雯 
Teacher work year is 3 
*/