The $this keyword

The $this keyword is used to get the class's own properties and method inside the class.

<?php

class Car {
    // The properties
    public $comp;
    public $color = "beige";
    public $hasSunRoof = true;

    // The method hello
    public function hello()
    {
        return "Beep I am a <i>" . $this->comp . "</i>, and I ama <i> " . $this->color;
    }
}

// Create the objects
$bmw = new Car();
$mercedes = new Car();

// Set the properties
$bmw->comp = "BMW";
$bmw->color = "blue";

$mercedes->comp = "Mercedes";
$mercedes->color = "green";

// Call method hello
echo $bmw->hello();
echo $mercedes->hello();

Let us create a User class using the same approach above and practice what we have learned in Chapter 2.

<?php

class User {

    // The properties
    public $firstName;
    public $lastName;

    // A method called hello
    public function hello()
    {
        return "Hello " . $this->firstName . " " . $this->lastName;
    }
}

$user1 = new User();

// Set the properties
$user1->firstName = 'Joe';
$user1->lastName = 'Doe';

// Function hello()
echo $user1->hello();

We can create any number of classes like this. Let us create one more class to understand how $this works.

<?php

class Animal {

    // Class properties
    public $type;
    public $name;
    public $breed;

    // Class methods
    function createAnimal($type, $name, $breed) {
        $this->type = $type;
        $this->name = $name;
        $this->breed = $breed;
    }
}

$daisy = new Animal();
$daisy->type = "dog";
$daisy->name = "Daisy";
$daisy->breed = "pomerenian";

printf("<p>The %s named %s  is a %s.</p>", $daisy->type, $daisy->name, $daisy->breed);

Method Chaining

The $this keyword is also used for method and property chaining. Let us write some code to understand about method and property chaining using $this keyword.

<?php

class Car {

    public $tank;

    public function fill($float)
    {
        $this->tank = $float;
        return $this;
    }

    public function ride($float)
    {
        $miles = $float;
        $gallons = $miles / 50;
        $this->tank -= $gallons;
        return $this;
    }
}

$bmw = new Car();
$tank = $bmw->fill(10)->ride(40)->tank;

echo "The number of gallons left is " . $tank . " gals";

Let us create a User class that uses method chaining using similar as above.

<?php

class User {

    // Properties of the class
    public $firstName;
    public $lastName;

    // Method to say hello
    public function hello() 
    {
        return "Hello, " . $this->firstName . " " . $this->lastName;
    }

    // Method to register
    public function register()
    {
        echo $this->firstName . " " . $this->lastName  . " is registered. ";
        return $this;
    }

    // Method to send email
    public function mail()
    {
        echo "Emailed";
    }
}

$user1 = new User();
$user1->firstName = "Jon";
$user1->lastName = "Doe";

$user1->register()->mail();