README

Value Objects and Enums

Installation and documentation

• Available as [Composer] package [yomy/valueobject].

What is this library about

This library adds a ValueObject and EnumValueObject classes.

Examples of value object

Creating an object:

use YomY\ValueObject\ValueObject;
$object = ValueObject::instance(1);

Getting value from the object

$value = $object->getValue();

Objects with the same value are going to be the same object

$object1 = ValueObject::instance(1);
$object2 = ValueObject::instance(1);
//These two are the same objects ($object1 === $object2)

You can use type hinting in methods

public function doSomething(ValueObject $valueObject) {
    $value = $valueObject->getValue();
    ...
}

You can extend the object for more detailed type hinting

class UserId extends ValueObject {}
class DataId extends ValueObject {}
...
public function doSomething(UserId $userId, DataId $dataId) {
    ...
}

Objects of different class or variable type are different

$object1 = ValueObject::instance('');
$object2 = ValueObject::instance(null);
$object3 = ValueObject::instance(false);
$object4 = ExtendedValueObject::instance('');
$object5 = ExtendedValueObject::instance(null);
$object6 = ExtendedValueObject::instance(false);
//All of the above are different

Instead of a strong (===) comparison operator, you could also use the equals() method

$object1 = ValueObject::instance(1);
$object2 = ValueObject::instance(1);
$same = $object1->equals($object2); //true

Generally, unserialize of a value object is prohibited, as this would break the ability to compare objects by reference. However, you might have a case you don't care about strict comparison, and need to unserialize the object. You can add a WeakValueObjectTrait usage to your custom object, which will allow unserializing it, and also compare objects by the values instead of reference when using equals() method

class MyWeakObject extends ValueObject {
    use WeakValueObjectTrait;
}
...
$weakObject1 = MyWeakObject::instance(1);
$serializedWeakObject = serialize($weakObject1);
$weakObject2 = unserialize($serializedWeakObject);
//These two objects are "equal" but not the same
$weakObject1->equals($weakObject2); //true
//On regular value objects this would be false

Examples of Enum value object

Creating an enum object

use YomY\ValueObject\EnumValueObject;
class Category extends EnumValueObject {
    const FIRST = 1;
    const SECOND = 2;
    const THIRD = 3;
}

Creating enum objects

$category = Category::instance(Category::FIRST);

or by referring referring to key

$category = Category::FIRST();

You will get an error if you try to instantiate invalid value

$category = Category::instance('missing_value');
$category = Category::MISSING();

Examples of Positive Integer value object

As value objects are commonly used as identifiers for database entities with an integer key, positive int value object ensures a valid key object for this purpose

Creating an object:

use YomY\ValueObject\PositiveIntValueObject;
$object1 = PositiveIntValueObject::instance(1);
$object2 = PositiveIntValueObject::instance('1');
//These two are the same objects ($object1 === $object2)

Usually, the id key in the db cannot be a 0, so these objects are invalid:

$object = PositiveIntValueObject::instance(0);
$object = PositiveIntValueObject::instance('0');

Of course, as with a basic value object, it is intended to use these in extended classes.

class UserId extends PositiveIntValueObject {}
class DataId extends PositiveIntValueObject {}
$user = UserId::instance(42);
$data = DataId::instance(42);
//these two are not the same