PHP Enums `__toString` magic method

Question

I am wondering why it is not possible to provide an __toString implementation for enum.

IDE says "Enum may not include '__toString'". However it was the first thing I thought about once I created enum. Previously I used Value Objects encapsulating strings in my code, which utilized string casting when necessary. Now I would like to migrate 'em into enums, but those resist.

#[Immutable]
enum SaveKlinesFromApiQueue: string
{
    case DEFAULT = 'save_klines_from_api_queue';
    case PRIORITY = 'save_klines_from_api_priority_queue';

    public function __toString(): string
    {
        return $this->value;
    }
}

Answer 1

As chris mentions, magic methods are not allowed.

For the 2 most(?) common usecases:

To get the string value of a single one, you can just use ->value.

If you want the string values of all of them, just add a loop in a method:

    public static function strings(): array
    {
        $strings = [];
        foreach(self::cases() as $case) {
            $strings[] = $case->value;
        }
        return $strings;
    }

Answer 2

Implementing JsonSerializable works if your use-case involves converting an enum property to json.

enum ParameterTypeEnum implements \JsonSerializable
{
    case QUERY;
    case COOKIE;
    case HEADER;
    case PATH;

    public function getType(): string
    {
        return match($this) {
            ParameterTypeEnum::QUERY => 'query',
            ParameterTypeEnum::COOKIE => 'cookie',
            ParameterTypeEnum::HEADER => 'header',
            ParameterTypeEnum::PATH => 'path',
        };
    }

    public function jsonSerialize(): mixed
    {
        return $this->getType();
    }
}