PHP enums: backed enums, from() and tryFrom()

An enum (enumeration) declares a type that only accepts a closed list of values: a section of the gazette is FeteDuVillage, Meteo or FaitsDivers (village fair, weather, news in brief), and nothing else. Enums have existed since PHP 8.1.

enum Rubrique: string
{
    case FeteDuVillage = 'village-fair';
    case Meteo = 'weather';
    case FaitsDivers = 'news-in-brief';

    public function libelle(): string
    {
        return match ($this) {
            Rubrique::FeteDuVillage => 'Village fair',
            Rubrique::Meteo => 'Weather',
            Rubrique::FaitsDivers => 'News in brief',
        };
    }
}

$rubrique = Rubrique::from('weather');        // Rubrique::Meteo
$inconnue = Rubrique::tryFrom('sports');      // null
foreach (Rubrique::cases() as $case) { /* … */ }

With a string, a typo ('wether') goes unnoticed; with an enum, PHP rejects it. A “backed” enum (enum Rubrique: string) gives each case a value, handy for a URL segment or a database column: from() finds the case from its value and throws a ValueError if it doesn't exist, while tryFrom() returns null instead. For a value that comes from the user, like a segment of the address, tryFrom() lets you answer cleanly with a 404 page. An enum can have methods and implement an interface, and a match on its cases doesn't need a default: a forgotten case throws an UnhandledMatchError at runtime, as soon as it is met, instead of slipping through silently.