README

Provides truly immutable value objects and an immutable value bag, along with base Immutable and ValueObject classes for your own objects. It helps to prevent against the oversights described by the article Avoiding Quasi-Immutable Objects in PHP.

Overview

The base Immutable class protects against common oversights in PHP regarding immutables:

It defines final public function __set() and final public function __unset() to prevent adding and mutating undefined properties.
It defines final public function offsetSet() and final public function offsetUnset() to prevent adding and mutating values via ArrayAccess.
It prevents multiple calls to __construct() to re-initialize the object properties.

Further, the base ValueObject class with() method checks the types of all incoming values to make sure they are themselves immutable. It does so via the static methods on the Type class.

The Type class recognizes scalars and nulls as immutable. All other non-object values (such are resources and arrays) are rejected as mutable.

When it comes to objects, the Type class recognizes anything descended from Immutable as immutable, as well as DateTimeImmutable. To allow Type to recognize other immutable classes, call Type::register() with a variadic list of fully-qualified class names that you want to treat as immutable.

Making Your Own Immutable Value Objects

Note:

This package can only do so much to keep you from accidentally overlooking mutability. For example, The Immutable and ValueObject classes cannot prevent you from deliberately adding your own mutable behaviors. Likewise, it is not possible to prevent against using reflection to mutate an object from the outside.

To create your own immutable value object, extend ValueObject with your own properties.

use Immutable\ValueObject\ValueObject;

class Address extends ValueObject
{
    protected $street;
    protected $city;
    protected $region;
    protected $postcode;
}

Then add a with*() method to allow changing of those values on a clone of the object, using the protected with() method on the base ValueObject.

class Address extends ValueObject
{
    protected $street;
    protected $city;
    protected $region;
    protected $postcode;

    public function withChanged(
        string $street,
        string $city,
        string $region,
        string $postcode
    ) {
        return $this->with([
            'street' => $street,
            'city' => $city,
            'region' => $region,
            'postcode' => $postcode
        ]);
    }
}

Finally, use that method in the constructor to initialize the properties, and call parent::__construct() to finish initialization.

class Address extends ValueObject
{
    protected $street;
    protected $city;
    protected $region;
    protected $postcode;

    public function __construct(
        string $street,
        string $city,
        string $region,
        string $postcode
    ) {
        $this->withChanged($street, $city, $region, $postcode);
        parent::__construct();
    }

    public function withChanged(
        string $street,
        string $city,
        string $region,
        string $postcode
    ) : self
    {
        return $this->with([
            'street' => $street,
            'city' => $city,
            'region' => $region,
            'postcode' => $postcode
        ]);
    }
}

Warning:

If you do not call parent::__construct() then the Value Object will not know that it has been initialized, and it will be possible to call the constructor multiple time to re-initialize the object.

Now you have an immutable Value Object.

You may find it useful to add validation; do so in your with*() methods, either directly or by calling a validation mechanism.

    public function withChanged(
        string $street,
        string $city,
        string $region,
        string $postcode
    ) {

        $valid = AddressValidator::validate($street, $city, $region, $postcode);
        if (! $valid) {
            throw new \RuntimeException('address is not valid');
        }

        return $this->with([
            'street' => $street,
            'city' => $city,
            'region' => $region,
            'postcode' => $postcode
        ]);
    }

Provided Immutable Value Objects

This package provides several Value Objects, both as examples and for common usage.

CreditCard

use Immutable\ValueObject\CreditCard;

$creditCard = new CreditCard('5555-5555-5555-4444');

// reading
$creditCard->getNumber(); // '5555555555554444'
$creditCard->getBrand(); // 'VISA'

// changing
$newCreditCard = $creditCard->withNumber('4111-1111-1111-1111');
$newCreditCard->getNumber(); // '4111111111111111'
$newCreditCard->getBrand(); // 'MASTERCARD'

Email

use Immutable\ValueObject\Email;

$email = new Email('bolivar@example.com');

// reading
$email->get(); // 'bolivar@example.com'

// changing
$newEmail = $email->withAddress('boshag@example.net');
$newEmail->get(); // 'boshag@example.net'

Ip

use Immutable\ValueObject\Ip;

$ip = new Ip('127.0.0.1');

// reading
$ip->get(); // '127.0.0.1'

// changing
$newIp = $ip->withAddress('192.168.0.1');
$newIp->get(); // '192.168.0.1'

Isbn

use Immutable\ValueObject\Isbn;

$isbn = new Isbn('960-425-059-0');

// reading
$isbn->get(); // '960-425-059-0'

// changing
$newIsbn = $ip->withAddress('0-8044-2957-X');
$newIsbn->get(); // '0-8044-2957-X'

Uri\HttpUri

use Immutable\ValueObject\Uri\HttpUri;

$httpUri = new HttpUri(
    'http://boshag:bopass@example.com:8080/foo?bar=baz#dib'
);

// reading
$httpUri->getScheme(); // 'http'
$httpUri->getHost(); // 'example.com'
$httpUri->getPort(); // 8080
$httpUri->getUser(); // 'boshag'
$httpUri->getPass(); // 'bopass'
$httpUri->getPath(); // /'foo'
$httpUri->getQuery(); // 'bar=baz'
$httpUri->getFragment(); // 'dib'

// changing
$newHttpUri = $httpUri
    ->withScheme('https')
    ->withHost('example.net')
    ->withPort('8888')
    ->withUser('newuser')
    ->withPass('newpass')
    ->withPath('/foo2')
    ->withQuery('zim=gir')
    ->withFragment('irk');

$newHttpUri->get(); // 'https://newuser:newpass@example.net:8888/foo2/?zim=gir#irk'

Uuid

use Immutable\ValueObject\Uuid;

$uuid = new Uuid('12345678-90ab-cdef-1234-567890123456');

// reading
$uuid->get(); // '12345678-90ab-cdef-1234-567890123456'

// changing
$newUuid = $uuid->withIdentifier('11111111-1111-1111-1111-111111111111');
$newUuid->get(); // '11111111-1111-1111-1111-111111111111'

// create a new random UUIDv4 identifier
$uuidv4 = Uuid::newVersion4();

Immutable Bag

The Bag is for an arbitrary collection of immutable values, and can be useful for immutable representations of JSON data.

use Immutable\Bag;

$bag = new Bag(['foo' => 'bar']);
echo $bag->foo; // bar
echo $bag['foo']; // bar

$bag->foo = 'baz'; // ImmutableObjectException
$bag = $bag->with('foo', 'baz');
echo $bag->foo; // baz
echo $bag['foo']; // baz

unset($bag->foo); // ImmutableObjectException
$bag = $bag->without('foo');

$bag->dib; // Notice: $dib not defined

$bag = $bag->with('dib', ['zim', 'gir']);
foreach ($bag->dib as $key => $value) {
    echo "$key:$value,"; // 0:zim,1:gir,
}

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