Object-Oriented PHP

__sleep and __wakeup

These magic methods have been available since PHP 4 and are invoked by the variable handling functions serialize and unserialize. They control how an object is represented so that it can be stored and recreated. The way that you store or communicate an integer is fairly trivial, but objects are more complex than primitive data types. Just as the __toString method controls how an object is displayed to the screen, __sleep controls how an object will be stored. This magic method is invoked indirectly whenever a call to the serialize function is made. Cleanup operations such as closing a database connection can be performed within the __sleep method before an object is serialized.

Conversely, __wakeup is invoked by unserialize ...