/**
 * @method static self ENGLAND() 
 * @method static self USA() 
 */
class CountryEnum extends Enum
{
    protected static function getEnums(): array
    {
        return ['england', 'usa'];
    }

}

用法

静态方法必须始终大写

assert(CountryEnum::USA() === CountryEnum::USA());

function country(CountryEnum $country): string {
    return $country->value();
}

assert(country(CountryEnum::USA()) === 'usa');

将枚举值转换为对象

assert(CountryEnum::get('usa') === CountryEnum::USA());