__sleep() Method¶
__sleep() is a magic method: it is called when an object is being serialized, so that the object may be cleaned.
In particular, some resources, such as database connections or files cannot be serialized. They should be closed, stored as a path, and reopened later with __wakeup().
The __sleep() method is usually paired with the __wakeup() method.
__sleep() must return an array listing, as strings, the names of the properties that should be serialized. Any property left out of that array is discarded, and reset to its default value once the object is unserialized.
If __sleep() does not return an array, PHP emits a warning and null is serialized instead of the object’s properties.
__sleep() cannot return the names of private properties declared in a parent class: doing so raises a notice. __serialize() and __unserialize() should be used instead when finer control over the serialized data, or access to inherited private properties, is needed.
<?php
class X {
private $file;
private $path;
function __sleep() {
fclose($this->file);
return ['path'];
}
function __wakeup() {
$this->file = fopen($this->path, 'r');
}
}
?>
See also PHP __sleep And __wakeup Magic Methods: How And When To Use Them?, __sleep() and __wakeup() and PHP’s __sleep() and __wakeup() Magic Methods for Serialization!.
Related : Magic Methods, __wakeup() Method, Serialization