PHP 8.4 Features: Property Hooks and array

PHP 8.4 was released in November 2024. Everything on this page needs PHP 8.4 or newer, so these examples cannot run on older versions (and not on this course’s local test server, which runs PHP 8.2). The code follows the official release notes at php.net/releases/8.4.

Property hooks

Property hooks let a property define its own get and set behaviour, so you often do not need separate getter and setter methods.

index.php

PHP

<?php
class Locale
{
    public string $languageCode;

    public string $countryCode
    {
        set (string $countryCode) {
            $this->countryCode = strtoupper($countryCode);
        }
    }

    public string $combinedCode
    {
        get => sprintf("%s_%s", $this->languageCode, $this->countryCode);
        set (string $value) {
            [$this->languageCode, $this->countryCode] = explode("_", $value, 2);
        }
    }

    public function __construct(string $languageCode, string $countryCode)
    {
        $this->languageCode = $languageCode;
        $this->countryCode = $countryCode;
    }
}

$locale = new Locale("en", "us");

echo $locale->combinedCode;   // en_US

A set hook runs when the property is assigned. It can clean or check the value.
A get hook runs when the property is read. It can calculate the value.
A property with only a get hook that does not use a stored value is a virtual property.

Asymmetric visibility

Control reading and writing separately: public to read, private (or protected) to write.

index.php

PHP

<?php
class PhpVersion
{
    public private(set) string $version = "8.4";

    public function increment(): void
    {
        [$major, $minor] = explode(".", $this->version);
        $minor++;
        $this->version = "{$major}.{$minor}";
    }
}

$v = new PhpVersion();
echo $v->version;      // readable from anywhere
// $v->version = "9";  // Error: cannot modify from outside

This removes a lot of “private property plus public getter” code.

new without extra parentheses

index.php

PHP

<?php
class PhpVersion
{
    public function getVersion(): string
    {
        return "PHP 8.4";
    }
}

echo new PhpVersion()->getVersion();   // no (new PhpVersion())-> needed

New array functions

array_find(), array_find_key(), array_any() and array_all() answer common questions without building a new array.

index.php

PHP

<?php
$animal = array_find(
    ["dog", "cat", "cow", "duck", "goose"],
    static fn(string $value): bool => str_starts_with($value, "c"),
);

var_dump($animal);   // string(3) "cat"

A fallback for older versions:

index.php

PHP

<?php
function findFirst(array $items, callable $test): mixed
{
    foreach ($items as $item) {
        if ($test($item)) {
            return $item;
        }
    }

    return null;
}

var_dump(findFirst(["dog", "cat", "cow"], fn($v) => str_starts_with($v, "c")));

Output

OUTPUT

string(3) "cat"

The #[\Deprecated] attribute

Marks your own functions, methods and class constants as deprecated, with a message. PHP then raises a deprecation notice when someone uses them.

index.php

PHP

<?php
class Report
{
    #[\Deprecated(message: "use Report::build() instead", since: "8.4")]
    public function make(): string
    {
        return $this->build();
    }

    public function build(): string
    {
        return "report";
    }
}

Other additions

Lazy objects: create an object whose initialisation runs only when it is first used. Mostly for frameworks.
HTML5 DOM: new Dom\HTMLDocument classes that parse HTML5 correctly, with querySelector().
mb_trim(), mb_ltrim(), mb_rtrim(), mb_ucfirst(), mb_lcfirst() for multibyte strings.
Object API for BCMath: BcMath\Number with operators.
request_parse_body() to read PUT and PATCH bodies.
DateTime::createFromTimestamp(), RoundingMode enum for round().

Deprecation to know

Declaring a parameter as Type $x = null (an implicit nullable type) is deprecated in 8.4. Write ?Type $x = null.

Should you use it?

If your host supports PHP 8.4, these are pleasant additions. If your code must also run on 8.3 or older, avoid them.

dangerous

Parse errors on older versions

Property hooks and asymmetric visibility are new syntax. On PHP 8.3 or older they stop the whole file from loading. Do not use them in code that older servers must run.