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.