PHP & MySQL® Web Development All-in-One Desk Reference for Dummies®

4.8. Copying Objects

PHP provides a method you can use to copy an object. The method is __clone, with two underscores. You can write your own __clone method in a class if you want to specify statements to run when the object is copied. If you don't write your own, PHP uses its default __clone method that copies all the properties as is. As shown by the two underscores beginning its name, the clone method is a different type of method, and thus is called differently, as shown in the following example.

You could write the following class:

class Car
{
  private $gas = 0;
  private $color = "red";
  function addGas($amount)
  {
     $this->gas = $this->gas + $amount;
     echo "$amount gallons added to gas tank";
  }
  function __clone()
  {
     $this->gas = 5;
  }
}

Using this class, you can create an object and copy it, as follows:

$firstCar = new Car;
$firstCar->addGas(10);
$secondCar = clone $firstCar;

After these statements, you have two cars:

• $firstCar: This car is red and contains 10 gallons of gas. The 10 gallons were added with the addGas method.

• $secondCar: This car is red, but contains 5 gallons of gas. The duplicate car is created using the __clone method in the Car class. This method sets gas to 5 and doesn't set $color at all.

If you didn't have a __clone method in the Car class, PHP would use a default __clone method that would copy all the properties, making $secondCar both red and containing 10 gallons of gas.