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Posted by reandeau on 08/16/06 22:16
Andy Hassall wrote:
> On 16 Aug 2006 14:38:57 -0700, "reandeau" <jon.tjemsland@gmail.com> wrote:
>
> >I'm building out a OO based app in PHP 5 but I'm getting a little
> >confused on children contructing parents.
> >
> >I have a parent that looks like this:
> >abstract Class State {
> > protected $database;
> > protected $user;
> > protected $output;
> > public function __construct($database,$user,$output) {
> > $this->database = $database;
> > $this->user = $user;
> > $this->output = $output;
> > }
> >}
> >
> >And a child that looks like this:
> >Class Status extends State {
> > public function __construct($database,$user,$output) {
> > parent::__construct($database,$user,$output);
> > }
> >}
> >
> >This seems to work OK. But I'm getting confused when thinking about
> >adding a new child who then has to contruct the parent again. Isn't
> >this getting away from the whole purpose of inheritence? It seems like
> >this is recreating the parent with every new child that come along.
> >Would it be possible to just have a single instance of the parent that
> >all children extended or am I missing the point here?
>
> You are possibly confusing "is-a" relationships between base class and
> subclass with a "has-a" relationship.
>
> Since Status "is a" State, then you need to do all the construction for the
> base class attributes first, then the construction for the subclass.
>
> There is no parent instance here - when you create a Status object, there is
> only one object; a Status object, which inherits everything that a State object
> has and can do, which then adds or overrides data and methods with data and
> methods deinfed in the State class.
>
> Now, if there is a common resource you want shared amongst all instances of
> the class, then that would be a "has-a" relationship - a variable in each class
> instance that is a reference to one separate instance of another object. A
> database connection might fall into this sort of category.
>
> --
> Andy Hassall :: andy@andyh.co.uk :: http://www.andyh.co.uk
> http://www.andyhsoftware.co.uk/space :: disk and FTP usage analysis tool
Thanks for the help. That makes sense.
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