Class/Object Functions

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# IX. Class/Object Functions

# Introduction

These functions allow you to obtain information about classes and instance objects. You can obtain the name of the class to which a object belongs, as well as its member properties and methods. Using these functions, you can find out not only the class membership of an object, but also its parentage (i.e. what class is the object class extending).

# Examples

In this example, we first define a base class and an extension of the class. The base class describes a general vegetable, whether it is edible or not and what is its color. The subclass `Spinach` adds a method to cook it and another to find out if it is cooked.

Example 1. classes.inc
    <?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

    ?>

We then instantiate 2 objects from these classes and print out information about them, including their class parentage. We also define some utility functions, mainly to have a nice printout of the variables.

Example 2. test_script.php
    <pre>
    <?php

    include "classes.inc";

    // utility functions

    function print_vars($obj) {
        $arr = get_object_vars($obj);
        while (list($prop, $val) = each($arr))
            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) {
        global $$obj;
        if (is_subclass_of($$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";
        }
    }

    // instantiate 2 objects

    $veggie = new Vegetable(true,"blue");
    $leafy = new Spinach();

    // print out information about objects
    echo "veggie: CLASS ".get_class($veggie)."\n";
    echo "leafy: CLASS ".get_class($leafy);
    echo ", PARENT ".get_parent_class($leafy)."\n";

    // show veggie properties
    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");
    ?>
    </pre>

One important thing to note in the example above is that the object `$leafy` is an instance of the class Spinach which is a subclass of Vegetable, therefore the last part of the script above will output:

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

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