PHP5 objects access/instantiation model (correction)

["Steve Perkins" <sp@xxxxxxxxxxxx>]

OK, so that came out fairly illegible. Try again:

Hi, new to PHP5 (and the forums evidently !) and I have a question about the
object model.

I want to be able to create a class which is allows abstraction from
specifics. So for one example, imagine a generic database connection wrapper
which can have multiple drivers depending on the database used. Some of the
functionality is generic, some is database specific (mysql_ , odbc_). So:

Class MySQL_driver {
        public prop1 ;
        public connect() {
                echo "Foo";
        }
        public runquery() {
                echo "Foo";
        }
        ...
}

Class ODBC_driver {
        public prop1 ;
        public connect() {
                echo "Foo";
        }
        public runquery() {
                echo "Foo";
        }
        ...
}

Class generic {
        public $driver = null ;
        function __construct($connection_type) {
                if $this->connection_type = "MySQL" {
                        $this->driver = new MySQL_Driver ;
                } else {
                        $this->driver = new ODBC_Driver ;
                }
        }

	// Using the non-generic connect() from the selected driver

        function authenticate {                                
                $this->driver->prop1 = "fooey"         

                // These references work fine from within
                // the generic class

                echo $this->driver->prop1 ;                    
                echo $this->driver->function1 ;
        }

	// Report non-generic errors from the selected driver

        function errors {                                              
        }
        function debug {
        }

        ...
               
}
       
$gen = new generic("MySQL") ;                          

// Instantiate the generic database object, which
// determines its own driver

$gen->driver->prop1 = "fooey"                          

// but they fail from here

echo $gen->driver->prop1 ;                     
echo $gen->driver->function1 ;

// this works ok though, so everything is created
// correctly

$gen->authenticate() ;                                 


So I want to access generic functions as $generic->authenticate(), and
database specific functions $generic->driver->runquery. This allows the top
level code to be able to be completely generic and not know anything about
the underlying database.

But I can't ! I can't find a way of accessing the encapsulated object
(driver) from the instantiator of generic. Is it possible ?

I guess there are lots of "workaround" ways. I could write lots of
"middleman" code in generic and use things like __set and __get etc but its
lots of extra overhead. I also know I could use extends but that makes the
code the wrong way around (MySQL_Driver would have to extend generic), hence
the top-level application would have to include code to determine which
driver to create rather than the db object determining its own connection
driver to use. This is true also for just lumping everything in a single
class per db type.

Surely it must be possible ? Or am I missing something ?

I also don't really get the idea of interface and abstract classes ? They
don't seem to be any practical use ? Maybe that's me ? Anyway, not really
relevant to this post ...

Please, please can someone help !!

Thanks

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