Enums — First-Class Enumerations (PHP 8.1)

TL;DR

Explanation

Two enum types: pure (unit) enums: enum Status { case Active; case Inactive; } and backed enums: enum Status: string { case Active = 'active'; case Inactive = 'inactive'; }. Methods, interfaces, and constants in enums. Static methods. from() / tryFrom() for backed enums. cases() returns all cases. Enums extend UnitEnum (pure) or BackedEnum (backed). Cannot be instantiated with new. Cannot extend classes. Enum cases are singletons — Status::Active === Status::Active always. In match expressions: exhaustive matching. In type hints: function process(Status $status). Compare with class constants: no type safety, no first-class status.

Common Misconception

Why It Matters

Common Mistakes

• Comparing enum cases with == instead of === — always use ===.
• Using string class constants as enum replacement — loses type safety.
• Not using tryFrom() for user input — from() throws on invalid value.

Code Examples

// Class constants — no type safety:
class Status {
    const ACTIVE = 'active';
    const INACTIVE = 'inactive';
}
function setStatus(string $status) {} // Accepts any string

enum Status: string {
    case Active = 'active';
    case Inactive = 'inactive';
}

function setStatus(Status $status): void {}
setStatus(Status::Active); // Type-safe

// User input:
$status = Status::tryFrom($request->input('status')) ?? Status::Active;

References

• ↗ https://www.php.net/manual/en/language.enumerations.php

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