introduction.md

Introduction

Classes

Classes are a unit of code organization in PHP. Code represents the behavior of an item or the behavior of a process can be grouped together as a class. Functions that are assigned to a class are called methods by convention.

<?php

class Door
{
    function lock()
    {
        // ...
    }

    function unlock()
    {
        // ...
    }
}

Classes are instantiated with the new keyword, this allocates memory for the class instance and calls the classes constructor method. Instantiated classes may be assigned to a variable. To invoke the methods of a class instance, we can use the -> access operator.

<?php

$a_door = new Door();
$a_door->lock();
$a_door->unlock();

An instantiated class may reference its own instance using the special $this variable. Classes may also have properties, these act as variables that are tied to the instance of the class object. These properties may be referenced internally or externally.

<?php

class Car
{
    public $color

    function __construct($color)
    {
        $this->color = $color;
    }

    function getColor()
    {
        return $this->color;
    }
}

$a_car = new Car("red");
$a_car->color; // => "red" by accessing the property
$a_car->getColor(); // => "red" by invoking the instance method