The Ultimate PHP Object Comparison Hack (Avoid Costly Mistakes!)

Comparing objects in PHP isn’t as straightforward as comparing numbers or strings. Objects store properties and methods, and their comparison depends on how they are instantiated and structured. In this guide, we’ll explore different ways to compare objects in PHP, the nuances behind == and ===, and best practices for object comparison.

Understanding Object Comparison in PHP

Unlike primitive data types, objects in PHP are compared based on their properties and identity. PHP provides two primary comparison operators:

• == (Equality Operator) → Compares object properties, ignoring reference identity.

• === (Identity Operator) → Compares both properties and reference identity.

Let’s break down these comparisons in detail.

Comparing Objects with == (Equality Operator)

The equality (==) operator checks if two objects have the same class and identical properties. However, it does not verify if they reference the same object in memory.

Example:

class Car {

    public $brand;

    public $model;

    public function __construct($brand, $model) {

        $this->brand = $brand;

        $this->model = $model;

    }

}

$car1 = new Car("Toyota", "Corolla");

$car2 = new Car("Toyota", "Corolla");

var_dump($car1 == $car2); // Output: bool(true)

Explanation:

• $car1 and $car2 are different objects.

• However, they have identical properties (brand and model have the same values), so == returns true.

Comparing Objects with === (Identity Operator)

The identity (===) operator checks whether two variables reference the exact same instance of an object.

Example:

$car3 = $car1;

var_dump($car1 === $car2); // Output: bool(false)

var_dump($car1 === $car3); // Output: bool(true)

Explanation:

• $car1 === $car2 returns false because even though they have the same values, they are different instances.

• $car1 === $car3 returns true because $car3 is just another reference to $car1.

Comparing Objects with Custom Methods

Sometimes, you may want a more flexible way to compare objects. You can define a custom method inside the class to compare only specific properties.

Example:

class Person {

    public $name;

    public $age;

    public function __construct($name, $age) {

        $this->name = $name;

        $this->age = $age;

    }

    public function isEqual(Person $otherPerson) {

        return $this->name === $otherPerson->name && $this->age === $otherPerson->age;

    }

}

$person1 = new Person("Alice", 25);

$person2 = new Person("Alice", 25);

$person3 = new Person("Bob", 30);

var_dump($person1->isEqual($person2)); // Output: bool(true)

var_dump($person1->isEqual($person3)); // Output: bool(false)

Why Use a Custom Comparison Method?

• You can customize the comparison logic based on specific needs.

• It provides better code readability and prevents unnecessary reliance on == or ===.

Deep Copy vs. Shallow Copy in Object Comparison

Shallow Copy

A shallow copy duplicates an object without creating a new instance of any referenced objects within it.

$car4 = clone $car1;

var_dump($car1 == $car4); // true

var_dump($car1 === $car4); // false

Deep Copy

A deep copy duplicates an object along with all referenced objects inside it.

class Engine {

    public $power;

    public function __construct($power) {

        $this->power = $power;

    }

}

class Vehicle {

    public $engine;

    public function __construct($power) {

        $this->engine = new Engine($power);

    }

    public function __clone() {

        $this->engine = clone $this->engine;

    }

}

$vehicle1 = new Vehicle(150);

$vehicle2 = clone $vehicle1;

var_dump($vehicle1 === $vehicle2); // false

var_dump($vehicle1->engine === $vehicle2->engine); // false

Best Practices for Object Comparison in PHP

1. Use === for strict identity checks. If you need to verify whether two variables refer to the exact same instance, always use ===.

2. Use == cautiously. This operator only checks if objects have the same properties, not if they are identical instances.

3. Implement custom comparison methods in classes when necessary to avoid relying solely on == or ===.

4. Consider object cloning strategies when working with deep or shallow copies.

Conclusion

Comparing objects in PHP requires a clear understanding of reference identity, property values, and how different operators work. While == checks for similar property values, === ensures objects are the same instance. Using custom methods for object comparison can offer greater flexibility and clarity in your code.

For more PHP tutorials, check out:

• Understanding PHP Superglobals

• PHP Constants and Their Usage

• PHP Operators Explained