Enum Methods

Enum Methods

Enum Methods, Interfaces and Constants

An enum can carry methods, static methods, constants and traits, and it can implement interfaces, so the rules about a status live next to its cases instead of in if chains across the codebase. Inside a method, $this is the current case. What an enum cannot have is state: declaring a property is a compile error ("Enum OrderStatus cannot include properties"), and it can neither extend nor be extended.

OrderStatus with a label interface, an alias constant and a static helperPHP

<?php
interface HasLabel { public function label(): string; }
enum OrderStatus: string implements HasLabel {
  case Pending = 'pending';  case Paid = 'paid';
  case Shipped = 'shipped';  case Cancelled = 'cancelled';
  const DEFAULT = self::Pending;                   // a constant may alias a case
  public function label(): string { return ucfirst($this->value); }   // $this is the case
  public static function open(): array { return [self::Pending, self::Paid]; }
}
echo OrderStatus::DEFAULT->label(), ' ', count(OrderStatus::open()), "\n";
var_dump(OrderStatus::Shipped instanceof HasLabel);

Output

Pending 2
bool(true)

Keep enum methods pure functions of the case: an enum that reads configuration or a database has become a service and belongs in a class (Interfaces and Generators).

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