Abstract data types as sum types

algebraic_data_types_as_sum_types.php

<?php

// define the classes:

class Remote {}

class UserDb {
    public $hash;
    function __construct($hash) {
        $this->hash = $hash;
    }
}

class PendingRequest {
    public $hash;
    function __construct($hash) {
        $this->hash = $hash;
    }
}

// define the sum type
type AuthenticationType = Remote | UserDb | PendingRequest;

enums_as_sum_types.php

<?php

// Enum's can be short-hand syntax for the above:
enum AuthenticationType {
    Remote,
    UserDb($hash),
    PendingRequest($hash)
}