Understanding PHP Magic Methods: __construct, __destruct, __call, and More

PHP provides a set of magic methods that are automatically invoked in specific object‑oriented scenarios, allowing developers to customize object behavior such as construction, destruction, property access, serialization, and more.

__construct()

Definition: class constructor.

Explanation: Called automatically when an object is instantiated; typically used to perform initialization tasks like assigning default values to properties.

class Person {
    public $name;
    public $age;
    public $sex;

    public function __construct($name = '', $sex = '男', $age = 28) {
        $this->name = $name;
        $this->sex = $sex;
        $this->age = $age;
    }
    // Note: If a subclass defines its own constructor, the parent constructor is not called automatically; use parent::__construct() to invoke it.
}

__destruct()

Definition: class destructor.

Explanation: Executed just before an object is destroyed, allowing cleanup actions such as closing files or releasing resources.

// Explicitly destroy an object
unset($obj);
// Or let the script end and PHP will call __destruct automatically.

__call()

Definition: invoked when calling an undefined or inaccessible instance method.

Explanation: Prevents fatal errors by handling calls to methods that do not exist, enabling graceful fallback logic.

public function __call($method, $args) {
    // handle undefined method calls
    echo "Method $method does not exist.";
}

__callStatic()

Definition: similar to __call() but triggered for undefined static method calls.

public static function __callStatic($method, $args) {
    echo "Static method $method does not exist.";
}

__get()

Definition: provides read access to inaccessible or private properties from outside the object.

Example:

private $name;

public function __get($property) {
    return $this->$property;
}

$person = new Person("小明", 60);
echo "姓名：" . $person->name; // triggers __get()

__set()

Definition: allows writing to inaccessible or private properties from outside the object.

public function __set($property, $value) {
    $this->$property = $value;
}

__isset()

Definition: invoked when isset() or empty() is called on an inaccessible property.

public function __isset($property) {
    echo "Checking if $property is set...<br>";
    return isset($this->$property);
}

isset($person->name);

__unset()

Definition: called when unset() is used on an inaccessible property.

public function __unset($property) {
    unset($this->$property);
}

__sleep()

Definition: executed automatically during serialize(); should return an array of property names to be serialized.

public function __sleep() {
    $this->name = base64_encode($this->name);
    return ['name', 'age'];
}

echo serialize($person);

__wakeup()

Definition: called automatically during unserialize(); can be used to re‑initialize resources.

public function __wakeup() {
    $this->name = base64_decode($this->name);
}

__toString()

Definition: defines how an object is converted to a string, e.g., when used with echo.

Note: Must return a string; throwing an exception inside will cause a fatal error.

public function __toString() {
    return "Person: {$this->name}, Age: {$this->age}";
}

echo $person; // triggers __toString()

__invoke()

Definition: allows an object to be called as a function.

public function __invoke() {
    echo "Calling object as a function!";
}

$person = new Person();
$person(); // triggers __invoke()

__set_state()

Definition: invoked when var_export() exports a class; should return an instance of the class.

public static function __set_state($array) {
    $obj = new self();
    foreach ($array as $key => $value) {
        $obj->$key = $value;
    }
    return $obj;
}

__clone()

Definition: called after an object is cloned.

public function __clone() {
    echo __METHOD__ . " you are cloning an object.<br>";
    $this->name = 'new name';
    $this->age = 18;
}

$copy = clone $person;

__autoload()

Definition: automatically loads undefined classes.

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

// Example usage
$a = new A();
$b = new B();

__debugInfo()

Definition: provides custom debug information for var_dump().

public function __debugInfo() {
    return [
        'message' => "姓名：{$this->name} 年龄：{$this->age}"
    ];
}

$person = new Person('tongfei', 28);
var_dump($person);