valueobject
Value Objects and Enums, (*1)
, (*2)
Installation and documentation
- Available as [Composer] package [yomy/valueobject].
What is this library about
This library adds a ValueObject and EnumValueObject classes., (*3)
Examples of value object
Creating an object:, (*4)
use YomY\ValueObject\ValueObject;
$object = ValueObject::instance(1);
Getting value from the object, (*5)
$value = $object->getValue();
Objects with the same value are going to be the same object, (*6)
$object1 = ValueObject::instance(1);
$object2 = ValueObject::instance(1);
//These two are the same objects ($object1 === $object2)
You can use type hinting in methods, (*7)
public function doSomething(ValueObject $valueObject) {
$value = $valueObject->getValue();
...
}
You can extend the object for more detailed type hinting, (*8)
class UserId extends ValueObject {}
class DataId extends ValueObject {}
...
public function doSomething(UserId $userId, DataId $dataId) {
...
}
Objects of different class or variable type are different, (*9)
$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, (*10)
$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, (*11)
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, (*12)
use YomY\ValueObject\EnumValueObject;
class Category extends EnumValueObject {
const FIRST = 1;
const SECOND = 2;
const THIRD = 3;
}
Creating enum objects, (*13)
$category = Category::instance(Category::FIRST);
or by referring referring to key, (*14)
$category = Category::FIRST();
You will get an error if you try to instantiate invalid value, (*15)
$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, (*16)
Creating an object:, (*17)
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:, (*18)
$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., (*19)
class UserId extends PositiveIntValueObject {}
class DataId extends PositiveIntValueObject {}
$user = UserId::instance(42);
$data = DataId::instance(42);
//these two are not the same
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