note 68245 deleted from language.oop5.interfaces by felipe
| From: | felipe@php.net | Date: | Tue, 11 Dec 2007 01:03:41 +0000 |
| Subject: | note 68245 deleted from language.oop5.interfaces by felipe | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-133349@lists.php.net to get a copy of this message | ||
Note Submitter: albert at friendly dot net
----
Maybe this is a bit like cyrille.berliat's problem plus a somewhat solution.
Let's say we want to create a queue class (or a stack, or a double
linked list, the usual... :-).
Wouldn't it be nice if we could define a generic interface or abstract (base) class that
dictates the way specific queues have to look like ?
Without having to specify the type of data to be queued.
But we _do_ want to be strict about the type of data to be passed to a specific queue type.
In other words: a bit of generic programming.
Alas, it seems that Type Hinting and Interface/abstract don't get along :(
But there might be a more runtime-involved solution. See below.
So, this won't work:
------
abstract class Object {} // as PHP(5) doesn't have a super-Object-base-class
class Cdata extends Object { } // i.e. Cdata IS-A Object
interface Iqueue {
public function enqueue(Object $data);
}
class Cmyqueue implements Iqueue {
public function enqueue(Cdata $data) { }
}
$q = new Cmyqueue;
$data = new Cdata;
$q->enqueue($data);
------
Nor will this 'compile':
------
abstract class Object {}
class Cdata extends Object {}
abstract class Iqueue extends Object {
abstract public function enqueue(Object $data);
}
class Cmyqueue extends Iqueue {
public function enqueue(Cdata $data) { }
}
$q = new Cmyqueue;
$data = new Cdata;
$q->enqueue($data);
---------
This however is possible:
abstract class Object {}
class Cdata extends Object
{
function __toString() { return('data'); }
}
abstract class Iqueue extends Object {
abstract public function enqueue(Object $data);
}
class Cmyqueue extends Iqueue {
public function enqueue(Object $data)
{ echo "enqueue '".$data->__toString()."'\n"; }
}
or:
interface Iqueue {
public function enqueue(Object $data);
}
class Cmyqueue implements Iqueue {
....
}
We could do our special Cmyqueue specific pre-processing before enqueu()ing.
But the compiler won't warn us if we pass anything other than the
object we expect to be passed.
We'd have to do something runtime like this:
class Cmyqueue extends Iqueue {
private function checkObjectType(Object &$obj)
{
if (get_class($obj) !== 'Cdata')
throw new Exception("You can only pass CData's to Cmyqueue");
}
public function enqueue(Object $data)
{
$this->checkObjectType($data);
echo "enqueue '".$data->__toString()."'\n";
}
}
hope this clears up some...