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PHP Constructors and Destructors

A constructor is a special method that runs when an object is created. A destructor is a special method that runs when an object is removed.

A constructor runs at creation

The Born line is printed inside __construct. It appears with no method call after the new line.

<?php
class Dog {
  public $name = "";
  public function __construct($name) {
    $this->name = $name;
    echo "Born: " . $this->name . "\n";
  }
}
$dog = new Dog("Rex");

Two objects, two births

Each new line runs __construct for its own object. The Born lines keep the order of the new lines.

<?php
class Dog {
  public $name = "";
  public function __construct($name) {
    $this->name = $name;
    echo "Born: " . $this->name . "\n";
  }
}
$first = new Dog("Rex");
$second = new Dog("Bella");

unset runs the destructor

unset drops the variable and removes its object. The Gone line prints before the line written after unset.

<?php
class Dog {
  public $name = "";
  public function __construct($name) {
    $this->name = $name;
  }
  public function __destruct() {
    echo "Gone: " . $this->name . "\n";
  }
}
$dog = new Dog("Rex");
unset($dog);
echo "After unset\n";

Example

<?php
class Car {
  public $year = 0;
  public function __construct($year) {
    $this->year = $year;
    echo "Born: " . $this->year . "\n";
  }
  public function park() {
    echo "Parked\n";
  }
  public function __destruct() {
    echo "Gone: " . $this->year . "\n";
  }
}
$car = new Car(2020);
$car->park();
unset($car);

Key points

  • The name __construct marks the constructor method.
  • The values in the new line reach __construct as its parameters.
  • __construct runs once for each object at its creation.
  • The name __destruct marks the destructor method.
  • A destructor runs when its object is removed.

In this example, __construct stores the year and prints the Born line. The park method prints its line next. unset then removes the car, and __destruct prints the Gone line.

Note

An object still alive at the end of a program is removed when the program ends.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz PHP Compiler

Exercise

When does __construct run?