What is $this in PHP (original) (raw)

Summary: in this tutorial, you will learn about PHP $this keyword and how to use $this inside a class to reference the current object.

In PHP, $this keyword references the current object of the class. The $this keyword allows you to access the properties and methods of the current object within the class using the object operator (->):

$this->property $this->method()Code language: PHP (php)

The $this keyword is only available within a class. It doesn’t exist outside of the class. If you attempt to use the $this outside of a class, you’ll get an error.

When you access an object property using the $this keyword, you use the $ with the this keyword only. And you don’t use the $ with the property name. For example:

$this->balanceCode language: PHP (php)

The following shows the BankAccount class:

`<?php

class BankAccount { public $accountNumber;

public $balance;

public function deposit($amount)
{
    if ($amount > 0) {
     <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mi>h</mi><mi>i</mi><mi>s</mi><mo>−</mo><mo>&gt;</mo><mi>b</mi><mi>a</mi><mi>l</mi><mi>a</mi><mi>n</mi><mi>c</mi><mi>e</mi><mo>+</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">this-&gt;balance += </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">hi</span><span class="mord mathnormal">s</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&gt;</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">ba</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">an</span><span class="mord mathnormal">ce</span><span class="mord">+</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>amount;
    }
}


public function withdraw($amount)
{
    if ($amount <= $this->balance) {
     <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mi>h</mi><mi>i</mi><mi>s</mi><mo>−</mo><mo>&gt;</mo><mi>b</mi><mi>a</mi><mi>l</mi><mi>a</mi><mi>n</mi><mi>c</mi><mi>e</mi><mo>−</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">this-&gt;balance -= </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">hi</span><span class="mord mathnormal">s</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&gt;</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">ba</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">an</span><span class="mord mathnormal">ce</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>amount;
        return true;
    }
            return false;

}

}`Code language: PHP (php)

Try it

In this example, we access the balance property via the $this keyword inside the deposit() and withdraw() methods.

Chaining methods #

First, create a new BankAccount object:

`// create a new account object $account = new BankAccount();

$account->accountNumber = 1; $account->balance = 100;`Code language: PHP (php)

Second, call the deposit() method three times to deposit different amounts of money:

$account->deposit(100); $account->deposit(200); $account->deposit(300);Code language: PHP (php)

This code is quite verbose. It would be more concise and expressive if you can write these statements using a single statement like this:

$account->deposit(100) ->deposit(200) ->deposit(300);Code language: PHP (php)

This technique is called method chaining.

To form the chain, the deposit() method needs to return a BankAccount object, which is the $this inside the BankAccount class like this:

`<?php

class BankAccount { public $accountNumber; public $balance;

public function deposit($amount)
{
    if ($amount > 0) {
     <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mi>h</mi><mi>i</mi><mi>s</mi><mo>−</mo><mo>&gt;</mo><mi>b</mi><mi>a</mi><mi>l</mi><mi>a</mi><mi>n</mi><mi>c</mi><mi>e</mi><mo>+</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">this-&gt;balance += </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">hi</span><span class="mord mathnormal">s</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&gt;</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">ba</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">an</span><span class="mord mathnormal">ce</span><span class="mord">+</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>amount;
    }
    return $this;
}

public function withdraw($amount)
{
    if ($amount <= $this->balance) {
     <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mi>h</mi><mi>i</mi><mi>s</mi><mo>−</mo><mo>&gt;</mo><mi>b</mi><mi>a</mi><mi>l</mi><mi>a</mi><mi>n</mi><mi>c</mi><mi>e</mi><mo>−</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">this-&gt;balance -= </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">hi</span><span class="mord mathnormal">s</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&gt;</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">ba</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">an</span><span class="mord mathnormal">ce</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>amount;
        return true;
    }
            return false;

}

}`Code language: PHP (php)

The deposit() returns the $this which is the current object of the BankAccount class. Therefore, you can call any public method of the BankAccount class.

The following example calls the deposit() method first and then the withdraw() method in a single statement:

$account->deposit(100) ->withdraw(150);Code language: PHP (php)

It’s equivalent to the following:

$account->deposit(100); $account->withdraw(150);Code language: PHP (php)

Put it all together:

`<?php

class BankAccount { public $accountNumber; public $balance;

public function deposit($amount)
{
    if ($amount > 0) {
     <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mi>h</mi><mi>i</mi><mi>s</mi><mo>−</mo><mo>&gt;</mo><mi>b</mi><mi>a</mi><mi>l</mi><mi>a</mi><mi>n</mi><mi>c</mi><mi>e</mi><mo>+</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">this-&gt;balance += </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">hi</span><span class="mord mathnormal">s</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&gt;</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">ba</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">an</span><span class="mord mathnormal">ce</span><span class="mord">+</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>amount;
    }
    return $this;
}

public function withdraw($amount)
{
    if ($amount <= $this->balance) {
     <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mi>h</mi><mi>i</mi><mi>s</mi><mo>−</mo><mo>&gt;</mo><mi>b</mi><mi>a</mi><mi>l</mi><mi>a</mi><mi>n</mi><mi>c</mi><mi>e</mi><mo>−</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">this-&gt;balance -= </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">hi</span><span class="mord mathnormal">s</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">&gt;</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.7778em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">ba</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">an</span><span class="mord mathnormal">ce</span><span class="mord">−</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>amount;
        return true;
    }
            return false;

}

}

// create a new account object $account = new BankAccount();

$account->accountNumber = 1; $account->balance = 100;

$account->deposit(100) ->withdraw(150);

echo "The bank account account−>accountNumberhasabalanceofaccount->accountNumber has a balance of account−>accountNumberhasabalanceof$account->balance";`Code language: PHP (php)

Try it

Summary #

PHP $this keyword references the current object of the class. It’s only available within the class.
Do use the method chaining by returning $this from a method to make the code more concise.

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