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Value Object

License

Overview

A Value Object (VO) is a type that is distinguishable only by the state of its properties. Unlike an entity, which has a unique identifier and remains distinct even if its properties are identical, VOs with the same properties are considered equal.

More details about VOs.

Installation

composer require tiny-blocks/value-object

How to use

The library exposes the ValueObject interface, which defines structural equality via equals(), and the ValueObjectBehavior trait, which provides a default implementation.

Concrete implementation

Declare your VO as final readonly class to let PHP enforce immutability at the language level.

<?php

namespace Example;

use TinyBlocks\Vo\ValueObject;
use TinyBlocks\Vo\ValueObjectBehavior;

final readonly class TransactionId implements ValueObject
{
    use ValueObjectBehavior;

    public function __construct(private string $value)
    {
    }
}

Using the equals method

The equals method compares two VOs by class and property values, returning true when both match.

$transactionId = new TransactionId(value: 'e6e2442f-3bd8-421f-9ac2-f9e26ac4abd2');
$otherTransactionId = new TransactionId(value: 'e6e2442f-3bd8-421f-9ac2-f9e26ac4abd2');

$transactionId->equals(other: $otherTransactionId); # true

Equality is strict: two VOs of different classes with the same property values are not considered equal, even when their shapes match.

final readonly class OrderId implements ValueObject
{
    use ValueObjectBehavior;

    public function __construct(private string $value)
    {
    }
}

$transactionId = new TransactionId(value: 'e6e2442f-3bd8-421f-9ac2-f9e26ac4abd2');
$orderId = new OrderId(value: 'e6e2442f-3bd8-421f-9ac2-f9e26ac4abd2');

$transactionId->equals(other: $orderId); # false

FAQ

01. Why does final readonly class matter?

Declaring a VO as final readonly class makes immutability a language-level guarantee: the PHP runtime rejects any attempt to mutate properties after construction, without requiring additional runtime checks. This is the recommended form for all new VOs.

02. How is equality determined?

Two VOs are considered equal when they are instances of the same class and all their properties have the same values, compared strictly. Different classes are never equal, even when their property shapes match.

License

Value Object is licensed under MIT.

Contributing

Please follow the contributing guidelines to contribute to the project.