PHP 8.1: What's New, Release History & Support Lifecycle

Enumerations (Enums)

Enums provide a clean way to define a set of named values with built-in type safety.

enum Suit {
    case Hearts;
    case Diamonds;
    case Clubs;
    case Spades;
}

function describe(Suit $suit): string { ... }

Readonly Properties

Properties declared as readonly can be written only once, usually in the constructor, making objects truly immutable after creation.

class Post {
    public readonly string $title;
    public readonly int $id;

    public function __construct(string $title, int $id) {
        $this->title = $title;
        $this->id = $id;
    }
}

First-Class Callable Syntax

A simpler way to create callables from functions or methods using the ... syntax.

$callable = strlen(...);
$method = $object->method(...);

New in Initializers

Objects and complex expressions can now be used in default values for parameters, properties, and constants.

function test(array $data = new ArrayObject()) { ... }

Pure Intersection Types

Combine multiple types that a value must satisfy using &.

function iterate(Traversable & Countable $items) { ... }

Never Return Type

Indicates a function never returns normally (it exits or throws).

function redirect(string $url): never {
    header("Location: $url");
    exit;
}

Final Class Constants

Class constants can be marked final to prevent overriding in child classes.

class ParentClass {
    final public const VALUE = "fixed";
}

Fibers

Fibers introduce lightweight cooperative concurrency, allowing code to be paused and resumed.

They help implement advanced async patterns without complex callbacks.

Array Unpacking with String Keys

The spread operator now works with arrays that have string keys.

$array = ['a' => 1, ...$anotherArray];

Explicit Octal Notation

Octal numbers now require the 0o prefix for clarity.

$value = 0o77; // equals 63