Re: Dynamically determine class

Norbert Wenzel wrote:

Hi, I'm using PHP5 and try to do something like this: I have a base class called 'Entry' and a child class called 'ExtendedEntry'. I want to read all Entries to a certain topic from a database. While constructing the EntryObject I would like to look if Entry is a simple Entry or an ExtendedEntry. I want the new object to be an ExtendedEntry - if possible - and otherwise to be an Entry. It was not possible to return the object in the __construct() function and it was not possible to reassign $this with code like

    $this = new ExtendedEntry()
also in the __construct() function. And I tried to always generate an ExtendedEntry with a flag, that says it is really Extended and a typecast afterwards, but I wasn't able to typecast to another object by (Entry) $extEntry.

Any suggestions how to solve this problem without writing a generateEntry() function, that looks into the database and then calls the correct class type?

no not really - although I would suggest to create a static member function (method) in the base class that acts as the factory e.g: class Entry { static public function create($key = array(), $type = null) { // $type could be used to force the type of class // or specify a class for a new object (as opposed to // an object created from existing database content // $key could be used to pass the relevant primary key(s) // in order to retrieve the relevant data. (leave empty to create // a 'new' object?) } } actually you might try looking into the delegation pattern which could offer an alternative to a factory function (i.e. the object can make extra methods from contained/helper classes available depending on the type of data retrieved)

thanks in advance, Norbert