Value Objects in PHP: Stop Writing Primitive-Obsessed Code

Why two $1000 bills aren't equal, and how to fix it with OOP. Colleagues, let's face it: our business logic often drowns in a sea of primitive types. string $email, float $amount, string $coordinates. It seems simple, but this very simplicity becomes a source of errors. The Problem: Primitive Obsession Imagine you are working with monetary amounts. Here is the typical code I've seen hundreds of times: class Order { public function __construct( private float $amount, private string $currency ) {} public function isEqual(Order $order): bool { // Compare two orders by amount and currency return $this->amount === $order->amount && $this->currency === $order->currency; } } Seems logical, right? Let's test it: $order1 = new Order(100.0, 'USD'); $order2 = new Order(100.0, 'USD'); var_dump($order1->isEqual($order2)); // bool(true) - all good so far $order3 = new Order(100.0, 'USD'); $order4 = new Order(100.00, 'USD'); // Same meaning, but... var_dump($order3->isEqual($order4)); // bool(true) - still ok. // Now here comes the problem: $order5 = new Order(0.1 + 0.2, 'USD'); // 0.30000000000000004 $order6 = new Order(0.3, 'USD'); // 0.3 var_dump($order5->isEqual($order6)); // bool(false) - OOPS! The problems are clear: Floating-Point Precision: Using float for money is a classic mistake. Unvalidated Data: We can create an order with the currency 'BLABLA'. Logic Duplication: Every time we compare orders, we must remember the rule for comparing currencies. Low Semantic Value: float and string don't communicate our intentions. Floating-Point Precision: Using float for money is a classic mistake. Unvalidated Data: We can create an order with the currency 'BLABLA'. Logic Duplication: Every time we compare orders, we must remember the rule for comparing currencies. Low Semantic Value: float and string don't communicate our intentions. The Solution: Value Object to the Rescue A Value Object is a small, immutable object that represents a descriptive aspect of the domain with no conceptual identity. Its key properties: It is defined by the composition of all its attributes. It is Immutable. Once created, it cannot be changed. It has no Identity. Two Value Objects are equal if all their fields are equal. It is defined by the composition of all its attributes. It is Immutable. Once created, it cannot be changed. It has no Identity. Two Value Objects are equal if all their fields are equal. Let's rewrite our example by creating a Money Value Object. class Money { public function __construct( private readonly int $amountInCents, // Store in cents to avoid float issues private readonly string $currency ) { // Validation in the constructor! The object cannot be created in an invalid state. if ($this->amountInCents < 0) { throw new InvalidArgumentException('Amount cannot be negative.'); } if (!in_array($this->currency, ['USD', 'EUR', 'GBP'])) { throw new InvalidArgumentException('Unsupported currency.'); } } // Objects must be self-comparable. public function equals(self $other): bool { return $this->amountInCents === $other->amountInCents && $this->currency === $other->currency; } // Example of business logic encapsulated within the VO public function add(self $other): self { if ($this->currency !== $other->currency) { throw new InvalidArgumentException('Cannot add different currencies.'); } return new self( $this->amountInCents + $other->amountInCents, $this->currency ); } // Create convenient factory methods (optional, but very useful) public static function fromUSD(float $amount): self { return new self((int) round($amount * 100), 'USD'); } public static function fromEUR(float $amount): self { return new self((int) round($amount * 100), 'EUR'); } // Getters if needed public function getAmount(): float { return $this->amountInCents / 100; } public function getCurrency(): string { return $this->currency; } } Now our Order class becomes elegant and reliable: class Order { public function __construct( private Money $total // Clear and understandable! ) {} public function isEqual(Order $order): bool { // All comparison logic is encapsulated in Money! return $this->total->equals($order->total); } } // Usage: $order1 = new Order(Money::fromUSD(100.0)); $order2 = new Order(Money::fromUSD(100.0)); var_dump($order1->isEqual($order2)); // bool(true) $order3 = new Order(Money::fromUSD(0.1)->add(Money::fromUSD(0.2))); $order4 = new Order(Money::fromUSD(0.3)); var_dump($order3->isEqual($order4)); // bool(true) - HOORAY! What benefits have we gained? Type Safety: You can no longer just pass a number. You need a Money object. Guaranteed Validity: If the object exists, it is correct. Encapsulated Logic: All money operations (addition, comparison) live in one place. Testability: It's easy to write unit tests for Money. Expressiveness: The code is self-documenting. Money $total says more than float $amount. Type Safety: You can no longer just pass a number. You need a Money object. Guaranteed Validity: If the object exists, it is correct. Encapsulated Logic: All money operations (addition, comparison) live in one place. Testability: It's easy to write unit tests for Money. Expressiveness: The code is self-documenting. Money $total says more than float $amount. Where else to use Value Objects? Email: Instead of string. It will validate the format. GeoPoint: Instead of two floats for latitude and longitude. DateRange: An object representing a period with a start and end. PersonName: An object that encapsulates first and last name, ensuring their correctness. Email: Instead of string. It will validate the format. GeoPoint: Instead of two floats for latitude and longitude. DateRange: An object representing a period with a start and end. PersonName: An object that encapsulates first and last name, ensuring their correctness. Conclusion Value Objects are not just "syntactic sugar." They are a powerful tool for domain modeling that allows you to write code that not only works but also clearly expresses your intentions and protects itself from errors. Stop writing primitive-obsessed code. Start modeling your domain. Do you use Value Objects in your projects? Which ones have been the most useful? Share your thoughts in the comments! #PHP #ObjectOrientedProgramming #DDD #DomainDrivenDesign #SoftwareArchitecture #ValueObjects #BestPractices #CodeQuality

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Value Objects in PHP: Stop Writing Primitive-Obsessed Code

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