PHP 8.1 Enums: Introduction and Usage

PHP 8.1 introduces native support for enums, allowing developers to define a fixed set of constant values that can be type‑checked and used like classes.

enum Status { case DRAFT; case PUBLISHED; case ARCHIVED; }

Enums can be used as typed properties, providing compile‑time safety:

class BlogPost { public function __construct(public Status $status) {} }

Instances are created by passing an enum case:

$post = new BlogPost(Status::DRAFT);

Enums may define methods, which can be combined with match for expressive logic:

enum Status { case DRAFT; case PUBLISHED; case ARCHIVED; public function color(): string { return match($this) { Status::DRAFT => 'grey', Status::PUBLISHED => 'green', Status::ARCHIVED => 'red', }; } }

Method usage:

$status = Status::ARCHIVED; $status->color(); // 'red'

Static methods are also allowed:

enum Status { // … public static function make(): Status { // … } }

Enums can implement interfaces just like regular classes:

interface HasColor { public function color(): string; } enum Status implements HasColor { case DRAFT; case PUBLISHED; case ARCHIVED; public function color(): string { /* … */ } }

Backed enums associate each case with a scalar value (string or int):

enum Status: string { case DRAFT = 'draft'; case PUBLISHED = 'published'; case ARCHIVED = 'archived'; }

Access the scalar value via the read‑only value property and recreate an enum from a value using from or tryFrom :

$value = Status::PUBLISHED->value; // 'published' $status = Status::from('published'); $maybe = Status::tryFrom('unknown'); // null

All cases can be listed with Enum::cases() :

Status::cases(); // [Status::DRAFT, Status::PUBLISHED, Status::ARCHIVED]

Enums are objects (singletons), allowing identity comparison:

$a = Status::DRAFT; $b = Status::DRAFT; $a === $b; // true

Because enum cases are objects, they cannot be used directly as array keys:

$list = [ Status::DRAFT => 'draft' // error ];

Traits can be used in enums, but enums cannot contain properties and cannot override built‑in enum methods.

Reflection support includes ReflectionEnum , ReflectionEnumUnitCase , and ReflectionEnumBackedCase , and the helper function enum_exists() checks for enum definitions.

Enums and their cases can be annotated with attributes, and the read‑only name property provides the case name for debugging.