Question

I’ve a class that stores an array and save its content on __destruct() event. Is __destruct() invoked automatically when there are no other reference to the object as a “whole “or relative to the current class or script that use it? Example:

class Store
{
  public function set($key, $value) { $this->data[$key] = $value; }
  public function __destruct() { fwrite($this->handle, serialize($this->data)); }
}

class Consumer
{
   protected $store;
   public function __construct() { $this->store = new Store(); }
   public function __destruct() { $this->store->set('key', 'a'); }
}

// In external script...
$store = new Store();
$store->set('key', 'b');
new Consumer();

When __destruct() is called in this example? Twice? One? What is the value of key?

Answer 1

The destructor method will be called as soon as there are no other references to a particular object, or in any order during the shutdown sequence.

The consumer’s would be called first since it immediately has no reference. Then the store’s when the script exits:

• new Store() => Store construct
• new Consumer() => Consumer construct => Store construct
• (implicit delete of Consumer) => Consumer destruct => Store destruct
• script exit => Store destruct

This is per object. Each object that is created/destroyed will have the construct/destruct methods called.