New Object Model

In PHP 5 there is a new Object Model. PHP's handling of objects has been completely rewritten, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types (for instance integers and strings). The drawback of this method was that semantically the whole object was copied when a variable was assigned, or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value (one can think of a handle as an object's identifier).

Many PHP programmers aren't even aware of the copying quirks of the old object model and, therefore, the majority of PHP applications will work out of the box, or with very few modifications.

The new Object Model is documented at the Language Reference.

In PHP 5, function with the name of a class is called as a constructor only if defined in the same class. In PHP 4, it is called also if defined in the parent class.

See also the zend.ze1_compatibility_mode directive for compatibility with PHP 4.

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User Contributed Notes 3 notes

bdas at premiergroup dot uk dot com
16 years ago
Since PHP5 upgraded PHP to an OOP language, they CHANGED the metaphor so that when you copy an object, you just get a pointer to it (as in C# and Java) and so therefore they needed to make a way to CLONE objects as well in case you need a REAL copy of the object.

Most cases, clone is not needed, simply because a real copy of an object is usually not mandatory.  In special cases, object cloning can be used to save time in porting.
quinn at strangecode dot com
17 years ago
Here is another possible solution for migrating code to php 5 when using $this = 'something' reassignments. In my case, I had several classes  with methods that were self-instantiating with static calls. I was able to simply use a different variable: I changed $this to $_this and it worked the same because I copied an instance of the original object by reference using an instantiation factory method:

class DB {
    function &getInstance()
        static $instance = null;

        if ($instance === null) {
            $instance = new DB();

        return $instance;

In every method needing access to this object I assigned it to a temporary variable by reference:
    function doSomething ()
        $_this =& DB::getInstance();

        $_this->param['id'] = 123;

Which allows method calls or saving data back to the original object.

I originally created classes like this so I didn't need to keep track of instantiations or global objects. I could just call DB::doSomething() and the object is created dynamically or referenced from an already existing object.
15 years ago
You should be able to clone a object in compatibility of PHP4,PHP5 with:
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