Object Serialization
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PHP Manual

## OOP Changelog

Changes to the PHP 5 OOP model are logged here. Descriptions and other notes regarding these features are documented within the OOP 5 documentation.

Version | Description
--- | ---
5.3.0 | Changed: It's now possible to reference the class using a variable (e.g., echo $classname::constant;). The variable's value can not be a keyword (e.g., self, parent or static).
5.3.0 | Changed: An `E_WARNING` level error is issued if the magic overloading methods are declared static. It also enforces the public visibility requirement.
5.3.0 | Changed: Prior to 5.3.0, exceptions thrown in the __autoload function could not be caught in the catch block, and would result in a fatal error. Exceptions now thrown in the __autoload function can be caught in the catch block, with one proviso. If throwing a custom exception, then the custom exception class must be available. The __autoload function may be used recursively to autoload the custom exception class.
5.3.0 | Added: The __callStatic method.
5.3.0 | Added: heredoc and nowdoc support for class const and property definitions. Note: heredoc values must follow the same rules as double-quoted strings, (e.g., no variables within).
5.3.0 | Added: Late Static Bindings.
5.3.0 | Added: The __invoke method.
5.2.0 | Changed: The __toString method was only called when it was directly combined with echo() or print(). But now, it is called in any string context (e.g. in printf() with %s modifier) but not in other types contexts (e.g. with %d modifier). Since PHP 5.2.0, converting objects without a __toString method to string emits a `E_RECOVERABLE_ERROR` level error.
5.1.3 | Changed: In previous versions of PHP 5, the use of var was considered deprecated and would issue an `E_STRICT` level error. It's no longer deprecated, therefore does not emit the error.
5.1.0 | Changed: The __set_state static method is now called for classes exported by var_export().
5.1.0 | Added: The __isset and __unset methods.

Object Serialization
Namespaces
Classes and Objects
PHP Manual