PHP Typed Properties

Summary: in this tutorial, you wil learn how to define typed properties by adding type hints to class properties.

Introduction to the PHP typed properties

The following example defines the BankAccount class with a property called $balance:

class BankAccount
{
    public $balance;
}Code language: PHP (php)

The default value of the $balance property is null.

$account = new BankAccount();
var_dump($account->balance); // nullCode language: PHP (php)

PHP 7.4 allows you to type hints the class properties with any types except void and callable. For example:

class BankAccount
{
    public float $balance;
}Code language: PHP (php)

In this example, the $balance property has the type float. When you add the float type to $balance property, the following code causes an error:

$account = new BankAccount();
var_dump($account->balance); // nullCode language: PHP (php)

Error:

Fatal error: Uncaught Error: Typed property BankAccount::$balance must not be accessed before initializationCode language: plaintext (plaintext)

It doesn’t work because the $balance property now becomes uninitialized. The default value of the $balance property is not null like before. Notice that you can still create a new object with typed properties uninitialized.

To read from a typed property, you need to initialize it first. For example:

<?php

class BankAccount
{
    public float $balance;
}

$account = new BankAccount();
$account->balance = 0;

var_dump($account->balance); // 0Code language: PHP (php)

For properties with scalar types, you can initialize them in the declaration. For example:

<?php

class BankAccount
{
    public float $balance = 0;
}

$account = new BankAccount();
var_dump($account->balance); // 0Code language: PHP (php)

Alternatively, you can initialize the typed properties in the constructor of the class:

<?php

class BankAccount
{
    public float $balance = 0;

    public function __construct(float $balance)
    {
        $this->balance = $balance;
    }
}

$account = new BankAccount(100);
var_dump($account->balance); // 100Code language: PHP (php)

If you unset a typed property, its status will change back to uninitialized. Note that for an untyped property, its value will become null after unset. For example:

<?php

class BankAccount
{
    public float $balance = 0;

    public function __construct(float $balance)
    {
        $this->balance = $balance;
    }
}

$account = new BankAccount(0);
var_dump($account->balance); // 0

unset($account->balance);
var_dump($account->balance); // errorCode language: PHP (php)

Typed properties and strict types

In the following example, the constructor of the BankAccount expects a float. However, you can pass a string. In this case, PHP coerces the string to a float:

<?php

class BankAccount
{
    public float $balance = 0;

    public function __construct(float $balance)
    {
        $this->balance = $balance;
    }
}

$account = new BankAccount("100.5");
var_dump($account->balance); // 100.5Code language: PHP (php)

If you don’t want this behavior, you can disable it by declaring strict_types at the beginning of the file as follows:

<?php

declare(strict_types=1);

class BankAccount
{
    public float $balance = 0;

    public function __construct(float $balance)
    {
        $this->balance = $balance;
    }
}

$account = new BankAccount("100.25"); // error
var_dump($account->balance);Code language: PHP (php)

Error:

Fatal error: Uncaught TypeError: Argument 1 passed to BankAccount::__construct() must be of the type float, string given.Code language: plaintext (plaintext)

Summary

• Typed properties include modifiers (private, protected, and public) and types (except void and callable).
• Typed properties have uninitialized states, not null like untyped properties.