After reviewing the basic concepts of OOP I can show you some more advanced techniques:
PHP doesn't support persistent objects, in OOP persistent objects are objects that
keep its state and funcionality across multiple invocations of the application, this
means having the ability of saving the object to a file or database and then loading
the object back. The mechanism is known as serialization. PHP has a serialize method
which can be called for objects, the serialize method returns a string representation
of the object. However serialize saves the datamembers of the object but not the
In PHP4 if you serialize the object to string $s, then destroy the object, and then
unserialize the object to $obj you might still access the object methods! I don't
recommend this because (a) The documentation doesn't guarrantee this beahaviour so
in future versions it might not work. (b) This might lead to 'illusions' if you save
the serialized version to disk and exit the script. In future runs of the script
you can't unserialize the string to an object an expect the methods to be there
because the string representation doesn't have the methods!
Summarizing serializing in PHP is VERY useful to save the data members of an
object just that. (You can serialize asociative arrays and arrays to save them to
// Save $str to disk
//...some months later
//Load str from disk
You have the datamembers recovered but not the methods (according to the documentation).
This leads to $obj2->x as the only way to access the data members (you have no methods!) so
don't try this at home.
There're some ways to fix the problem, I leave it up to you because they are too dirty
for this neat article.
Full serialization is a feature I'd gladly welcome in PHP.