Mastering PHP Magic Methods: 16 Essential Tricks for Developers

PHP is a popular server‑side language, and magic methods—functions whose names start with double underscores—play a crucial role in object‑oriented programming.

- __construct(): class constructor - __destruct(): class destructor - __call($funName, $arguments): invoked when an undefined instance method is called - __callStatic($funName, $arguments): invoked when an undefined static method is called - __get($propertyName): invoked when reading an inaccessible property - __set($property, $value): invoked when writing to an inaccessible property - __isset($property): invoked when isset() or empty() is used on an inaccessible property - __unset($property): invoked when unset() is used on an inaccessible property - __sleep(): called before serialization to specify which properties should be serialized - __wakeup(): called after deserialization for reinitialisation - __toString(): defines how an object is converted to a string - __invoke(): allows an object to be called as a function - __set_state($array): used by var_export() to recreate an object - __clone(): called when an object is cloned - __autoload($className): attempts to load an undefined class - __debugInfo(): customises var_dump() output

1. __construct()

The constructor runs automatically after an object is created. If no constructor is defined, PHP provides a default one with no parameters.

function __construct([parameter list]) {
    // initialise properties
}

Example:

<?php
class Person {
    public $name;
    public $age;
    public $sex;
    public function __construct($name = "", $sex = "Male", $age = 22) {
        $this->name = $name;
        $this->sex  = $sex;
        $this->age  = $age;
    }
    public function say() {
        echo "Name: $this->name, Sex: $this->sex, Age: $this->age";
    }
}
$person1 = new Person();
$person1->say(); // Name: , Sex: Male, Age: 22
$person2 = new Person("James");
$person2->say(); // Name: James, Sex: Male, Age: 22
$person3 = new Person("Jack", "Male", 25);
$person3->say(); // Name: Jack, Sex: Male, Age: 25
?>

2. __destruct()

The destructor runs just before an object is destroyed, allowing cleanup such as closing files or releasing resources. It cannot accept parameters.

function __destruct() {
    // cleanup code
}
?>

Example:

<?php
class Person {
    public $name;
    public $age;
    public $sex;
    public function __construct($name = "", $sex = "Male", $age = 22) {
        $this->name = $name;
        $this->sex  = $sex;
        $this->age  = $age;
    }
    public function say() {
        echo "Name: $this->name, Sex: $this->sex, Age: $this->age";
    }
    public function __destruct() {
        echo "Well, my name is $this->name";
    }
}
$person = new Person("John");
unset($person); // triggers __destruct()
?>

3. __call()

When an undefined or inaccessible instance method is called, __call() receives the method name and an array of arguments.

function __call(string $function_name, array $arguments) {
    // handle missing method
}
?>

Example:

<?php
class Person {
    public function say() { echo "Hello, world!<br>"; }
    public function __call($funName, $arguments) {
        echo "The function you called: $funName (parameters: ";
        print_r($arguments);
        echo ") does not exist!<br>
";
    }
}
$person = new Person();
$person->run("teacher"); // triggers __call()
$person->eat("John", "apple"); // triggers __call()
$person->say();
?>

4. __callStatic()

Similar to __call(), but for undefined static methods.

public static function __callStatic($funName, $arguments) {
    // handle missing static method
}
?>

Example:

<?php
class Person {
    public static function __callStatic($funName, $arguments) {
        echo "The static method you called: $funName (parameters: ";
        print_r($arguments);
        echo ") does not exist!<br>
";
    }
}
Person::run("teacher");
Person::eat("John", "apple");
?>

5. __get()

Allows reading of inaccessible or private properties. It can return computed values.

public function __get($propertyName) {
    if ($propertyName == "age") {
        return ($this->age > 30) ? $this->age - 10 : $this->age;
    }
    return $this->$propertyName;
}
?>

Example usage prints "Name: John" and "Age: 50" when the internal age is 60.

6. __set()

Intercepts writes to inaccessible properties, allowing validation.

public function __set($property, $value) {
    if ($property == "age" && ($value > 150 || $value < 0)) {
        return; // reject illegal age
    }
    $this->$property = $value;
}
?>

7. __isset()

Called when isset() or empty() is used on an inaccessible property.

public function __isset($property) {
    echo "The {$property} property is private, __isset() called automatically.<br>";
    return isset($this->$property);
}
?>

8. __unset()

Invoked when unset() is called on an inaccessible property.

public function __unset($property) {
    echo "It is called automatically when we use unset() outside the class.<br>";
    unset($this->$property);
}
?>

9. __sleep()

Executed before serialization; returns an array of property names to be serialized.

public function __sleep() {
    echo "It is called when serialize() is invoked.<br>";
    $this->name = base64_encode($this->name);
    return array('name', 'age');
}
?>

10. __wakeup()

Executed after unserialization for reinitialisation.

public function __wakeup() {
    echo "It is called when unserialize() is invoked.<br>";
    $this->name = 2; // example reinitialisation
}
?>

11. __toString()

Defines how an object is converted to a string. Must return a string.

public function __toString() {
    return 'go go go';
}
?>

12. __invoke()

Allows an object to be called as a function.

public function __invoke() {
    echo 'This is an object';
}
?>

13. __set_state()

Called by var_export() to recreate an object from an array of properties.

public static function __set_state($array) {
    $obj = new self();
    $obj->name = $array['name'];
    return $obj;
}
?>

14. __clone()

Invoked when an object is cloned, allowing deep copy adjustments.

public function __clone() {
    echo __METHOD__ . " you are cloning the object.<br>";
}
?>

15. __autoload()

Automatically includes the file that defines an undefined class.

function __autoload($className) {
    $filePath = "project/class/{$className}.php";
    if (is_readable($filePath)) {
        require $filePath;
    }
}
?>

16. __debugInfo()

Customises the output of var_dump() for an object (available from PHP 5.6).

public function __debugInfo() {
    return ['propSquared' => $this->prop ** 2];
}
?>

These magic methods provide powerful hooks into PHP's object model, enabling developers to control object creation, property access, method calls, serialization, and debugging.