Changes to OO in PHP5

Support for objects in PHP goes all the way back to PHP3. There was never any intention of supporting the idea of classes or objects, but some limited support was added, almost as an afterthought, to provide "syntactic sugar'' (to use Zeev Suraski's phrase) for associative arrays. Object support in PHP was originally designed as a convenient way of grouping data and functions, but only a small subset of the features traditionally associated with a full-blown object-oriented programming language was included. As PHP grew in popularity, the use of an OO approach became increasingly common in large applications. However, the poor internal implementation became limiting.

Most notably, there was no support for real encapsulation. You could not specify member variables or methods to be private or protected. Everything was public which, as you've seen, can be problematic.

Additionally, there was no support for abstract interfaces or methods. Methods and member variables could not be declared static. There were no destructors. All these concepts are familiar to anyone with a background in another object-oriented programming language, and the lack of these features in PHP's object model could make the transition from a language such as Java (which does support all these ideas) to PHP difficult. For those who have previous experience with PHP4, the following table lists some of the new features in the PHP5 object model.

New Feature	Benefit
Private, protected member variables and methods	Real encapsulation and data protection are now possible in PHP.
Improved dereferencing support	Statements like $obj->getSomething()->doSomething() are now possible.
Static member variables and methods	Methods that can be called statically are now clearly identifiable. Class-level constants help control pollution of the global namespace.
Unified constructors	All class constructors are now called __construct(). This helps with encapsulation of overridden subclass constructors and makes it easier to alter inheritance when multiple classes are involved in a tree of inheritance.
Destructor support	Through the __destruct() method, classes in PHP can now have destructors. This feature allows actions to be carried out when the object is destroyed.
Support for abstract classes and interfaces	You can define required methods in a parent class while deferring implementation to a subclass. Abstract classes can't be instantiated; only their nonabstract subclasses can.
Parameter type hints	You can specify the class for function parameters that are expecting an object. function foo(Bar $objBar) { ... allows you to be sure that the data type of the parameter is what we expect.