Welcome back! We're continuing our journey into object-oriented programming (OOP) with a new and exciting topic: Polymorphism. You've already learned about classes, objects, and inheritance, which are essential building blocks of OOP. Now, it's time to explore how polymorphism can make your code more flexible and reusable.

Polymorphism allows objects to be treated as instances of their parent class rather than their actual class. This provides a way to use a single interface to represent different types of objects. Here’s what we’ll cover in this lesson:

1. Understanding Polymorphism: We'll discuss what polymorphism is and why it's a powerful concept in programming.
2. Implementing Polymorphism in PHP: You'll learn how to use method overriding and interfaces to achieve polymorphism.

Polymorphism in PHP allows you to call derived class methods through a parent class reference. This can make your code more dynamic and generic. For example, consider the following code snippet:

php
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1<?php
2
3// Define a base class Person with name and age attributes
4class Person {
5    protected $name;
6    protected $age;
7
8    public function __construct($name, $age) {
9        $this->name = $name;
10        $this->age = $age;
11    }
12
13    // Define a method to display details, meant to be overridden in derived classes
14    public function display() {
15        echo "Name: {$this->name}, Age: {$this->age}\n";
16    }
17}
18
19// Define a derived class Student with a major attribute
20class Student extends Person {
21    private $major;
22
23    public function __construct($name, $age, $major) {
24        parent::__construct($name, $age);
25        $this->major = $major;
26    }
27
28    // Override the display method to include the major attribute
29    public function display() {
30        parent::display();
31        echo "Major: {$this->major}\n";
32    }
33}
34
35// Define a derived class Teacher with a subject attribute
36class Teacher extends Person {
37    private $subject;
38
39    public function __construct($name, $age, $subject) {
40        parent::__construct($name, $age);
41        $this->subject = $subject;
42    }
43
44    // Override the display method to include the subject attribute
45    public function display() {
46        parent::display();
47        echo "Subject: {$this->subject}\n";
48    }
49}
50
51// Create instances of Student and Teacher using parent class references
52$person1 = new Student("Alice", 30, "Computer Science");
53$person2 = new Teacher("Bob", 25, "Mathematics");
54
55// Call the display method on the parent class references. The appropriate derived class method will be invoked.
56$person1->display();
57$person2->display();
58
59?>

In this example, the display method of the derived classes (Student and Teacher) overrides the method in Person. When we call display on a parent class reference, the appropriate derived class method is invoked.

Polymorphism is crucial because it introduces flexibility and scalability to your code:

• Code Flexibility: Polymorphism allows you to write functions that can operate on objects of different types through a common interface.
• Reusability: You can extend and reuse your code more efficiently by leveraging polymorphism.
• Simplified Code Management: Polymorphism helps you manage and understand your code better, as similar operations are handled in a unified manner.

Are you excited to dive into the practice section and apply polymorphism to your programs? Let's get started and see the power of this concept in action!