PHP Constructors & Destructors
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class ClassName {
function __construct($parameter = default_value) {
// runs when the object is created
}
function __destruct() {
// runs when the object is destroyed
}
}
$object = new ClassName($argument);What is a Constructor?
A constructor is a special method named __construct() that PHP calls automatically the moment an object is created with new, making it the natural place to initialize required properties or validate input.
Example: What is a Constructor?
<?php
// Define the class `User`
class User {
// Define the constructor `__construct` with no parameters
function __construct() {
// Print "User object created!" to the output
echo "User object created!";
}
}
new User();
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Constructors with Parameters
Constructor parameters let you require certain data up front, such as new User(Aditi, '[email protected]'), ensuring every object starts in a valid, fully-initialized state rather than needing manual setup afterward.
Example: Constructors with Parameters
<?php
// Define the class `User`
class User {
// Declare the public property `$name`
public $name;
// Declare the public property `$email`
public $email;
// Define the constructor `__construct` taking `$name`, `$email`
function __construct($name, $email) {
$this->name = $name;
$this->email = $email;
}
}
// Create a new `User` instance with 'Aditi', '[email protected]', stored in `$user`
$user = new User('Aditi', '[email protected]');
// Print `$user->name . " " . $user->email` to the output
echo $user->name . " " . $user->email;
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Default Values in Constructors
A destructor is a special method named __destruct() that PHP calls automatically when an object is about to be destroyed, typically at the end of a script or when nothing references it anymore.
Example: Default Values in Constructors
<?php
// Define the class `Logger`
class Logger {
// Define the magic method `__destruct` with no parameters
function __destruct() {
// Print "Logger destroyed" to the output
echo "Logger destroyed";
}
}
// Create a new `Logger` instance, stored in `$log`
$log = new Logger();
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What is a Destructor?
Destructors are most useful for cleanup tasks like closing a file handle or a database connection that the object opened, so resources don't leak even if the code that created the object forgets to close them explicitly.
Example: What is a Destructor?
<?php
// Define the class `FileHandler`
class FileHandler {
// Define the magic method `__destruct` with no parameters
function __destruct() {
// Print "Closing file handle" to the output
echo "Closing file handle";
}
}
// Create a new `FileHandler` instance, stored in `$file`
$file = new FileHandler();
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Constructor and Destructor Together
Unlike constructors, destructors are rarely written explicitly in typical PHP web code, since PHP's request lifecycle already cleans up resources at the end of each request — they matter more in long-running scripts.
Example: Constructor and Destructor Together
<?php
// Define the class `Task`
class Task {
// Define the constructor `__construct` with no parameters
function __construct() {
// Print "Task started\n" to the output
echo "Task started\n";
}
// Define the magic method `__destruct` with no parameters
function __destruct() {
// Print "Task finished" to the output
echo "Task finished";
}
}
// Create a new `Task` instance, stored in `$task`
$task = new Task();
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- Forgetting to call
parent::__construct()in a child class constructor, so the parent's setup does not run. - Naming the constructor after the class as in old PHP 4 style, when modern PHP uses
__construct. - Expecting the destructor to run at a specific time, when it runs when the last reference goes away or the script ends.
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