클래스 및 객체와 같은 PHP 변수 및 유형 확장

<?php
    // base class with member properties and methods
    class Vegetable {
        var $edible;
        var $color;
        function Vegetable($edible, $color="green") 
        {
            $this->edible = $edible;
            $this->color = $color;
        }
        function is_edible() 
        {
            return $this->edible;
        }
        function what_color() 
        {
             return $this->color;
        }
   } // end of class Vegetable
   // extends the base class
   class Spinach extends Vegetable {
       var $cooked = false;
       function Spinach() 
       {
           $this->Vegetable(true, "green");
       }
       function cook_it() 
       {
           $this->cooked = true;
       }
       function is_cooked() 
       {
           return $this->cooked;
       }
   } // end of class Spinach
?>

<?php
    include "classes.inc";
    // 实用函数
    function print_vars($obj)
    {
        foreach (get_object_vars($obj) as $prop => $val) {
            echo "\t$prop = $val\n";
        }
    }
    function print_methods($obj)
    {
        $arr = get_class_methods(get_class($obj));
        foreach ($arr as $method) {
            echo "\tfunction $method()\n";
        }
    }
    function class_parentage($obj, $class)
    {
        if (is_subclass_of($GLOBALS[$obj], $class)) {
            echo "Object $obj belongs to class " . get_class($$obj);
            echo " a subclass of $class\n";
        } else {
            echo "Object $obj does not belong to a subclass of $class\n";
        }
    }
    // 实例化 2 对象
    $veggie = new Vegetable(true, "blue");
    $leafy = new Spinach();
    // 打印这些对象的信息
    echo "veggie: CLASS " . get_class($veggie) . "\n";
    echo "leafy: CLASS " . get_class($leafy);
    echo ", PARENT " . get_parent_class($leafy) . "\n";
    // 显示蔬菜的属性
    echo "\nveggie: Properties\n";
    print_vars($veggie);
    // and leafy methods
    echo "\nleafy: Methods\n";
    print_methods($leafy);
    echo "\nParentage:\n";
    class_parentage("leafy", "Spinach");
    class_parentage("leafy", "Vegetable");
?>

[...]
Parentage:
Object leafy does not belong to a subclass of Spinach
Object leafy belongs to class spinach a subclass of Vegetable