ID: 35104
User updated by: php at tjworld dot net
Reported By: php at tjworld dot net
Status: Assigned
Bug Type: Class/Object related
Operating System: Windows 2003
PHP Version: 5.1.0RC5
Assigned To: dmitry
New Comment:
Thanks for the DOM-specific recommendations, I'll have a play about
with it.
The case for dynamic properties is a big issue in itself, since when
extending a class the developer doesn't always have control of the
internal design on the super-class.
This could lead to some frustrating situations where the developer has
every reasonable expectation they can extend the super-class, but in
use trying to modify a protected or public property causes this Fatal
Error.
It could also lead to intermitent results if the statement attempting
the modification is in a little-used method of the sub-class, and only
occurs on rare occasions.
Without compile-time access-checking (unlike a strongly typed
pre-compiled environment) these kind of issues could occur easily,
especially for the more general developers who aren't so au-fait with
the technicalities of PHP OO dynamic properties.
I was wondering if the properties affected by __set() should be marked
final, which would prevent inconsistencies but reduce functionality to
a great extent.
Maybe its a case of stressing in the documentation *not* to rely on
__set() to produce read-only properties *unless* the __set() method
first checks that the calling class-instance is an instanceof the
super-class - in other words the read-only functionality is conditional
on the method being called on an instance of the super-class itself, not
a sub-class.
This puts the ball back in the developer's court, but you'd need some
good strong documentation across the platform to ensure developers use
this design template.
Previous Comments:
------------------------------------------------------------------------
[2005-11-04 22:54:02] [EMAIL PROTECTED]
Cant say about other internal classes, but DOM is written specifically
not to allow overriding properties (properties provide direct access to
libxml2 functionality which cant be done in userland). As far as casting
goes... already working on a way to allow returning extended classes
from all functions in dom (for PHP 6).
Current workaround for your issue create your extended class using new
keyword, and append it to a DOMDocumentFragment (if you dont want it
linked into the document tree) that was created using
createDocumentFragment. The appending updates the libxml2 pointers and
the extended object is now linked to the DOMDocument correctly.
Was this report specific to dom or is it to remain open for the
extneded uses object example?
------------------------------------------------------------------------
[2005-11-04 21:39:48] php at tjworld dot net
"but DOM properties CANNOT be overriden."
Does this occur anywhere else in the PHP classes or is it unique to
DOM? It's the first time I've met this situation in OO since the 80's.
It pretty much makes having the DOM object-oriented pointless, when the
base class (DOMNode) of the other significant DOM classes prevents
useful extension.
A simple solution would be to provide a courtesy:
DOMNode->__construct($ownerDocument = null);
But that'd be available to the public of course. Alternatively,
protected DOMNode function _setOwnerDocument(DOMDocument
ownerDocument);
But thats a bit arbitary. Alternatively, solve the practical loss of
functionality by fixing the bug in importNode() so it returns an object
of the class passed in:
DOMNode DOMDocument->importNode(DOMNode $node, bool deep);
Currently it *casts* the passed $node to one of the DOM base classes it
inherited from *and* discards all their extended properties and methods,
which is surely not OO behaviour because in the following scenario, the
cases listed at the end are inconsistent:
class inChild extends DOMNode {}
class inGrandChild extends DOMElement()
class inGreatGrandChild extends inGrandChild()
$node = new DOMNode();
$element = new DOMElement();
$child = new inChild();
$grandChild = new inGrandChild();
$greatGrandChild = new inGreatGrandChild();
1. DOMDocument->importNode($node, true) instanceof DOMNode
2. DOMDocument->importNode($element, true) instanceof DOMElement
3. DOMDocument->importNode($child, true) instance of DOMNode
4. DOMDocument->importNode($grandChild, true) instanceof DOMElement
(not inGrandChild)
5. DOMDocument->importNode($greatGrandChild, true) instanceof
DOMElement (not inGreatGrandChild)
So importNode() doesn't even cast to a consistent DOMNode, but to the
'highest* level in the built-in classes.
Usually in OO although the cast is to a super-class (to guarantee
portability) the extended methods and properties aren't discarded.
If importNode() were fixed to return the same class as passed in the
following code would solve the ownerDocument issue:
<?php
class extDOMDocument extends DOMDocument {
public function createElement($name, $value=null) {
$orphan = new extDOMElement($name, $value);
$adopt = $this->importNode($ret, true); // adopt it
// now $adopt satisfies $this->isSameNode($adopt->ownerDocument) &&
$adopt instanceof extDOMelement
return $adopt;
}
}
class extDOMElement extends DOMElement {
function __construct($name, $value=null, $namespace=null) {
parent::__construct($name, $value, $namespaceURI);
}
// ... more class definition here
}
(excuse any typo's - working weird hours!)
------------------------------------------------------------------------
[2005-11-04 17:02:40] [EMAIL PROTECTED]
I can't speak for the user class example, but DOM properties CANNOT be
overriden.
------------------------------------------------------------------------
[2005-11-04 16:26:34] [EMAIL PROTECTED]
Dmitry, any insight on this?
------------------------------------------------------------------------
[2005-11-04 13:27:28] php at tjworld dot net
Further test using DOMDocument/DOMElement...
C:\PHP\5.1.0RC5-dev>php.exe dom.php
Fatal error: extDOMElement::__construct(): Cannot write property in
C:\dom.php on line 14
----------dom.php-------------
<?php
class extDOMDocument extends DOMDocument {
public function createElement($name, $value=null) {
$ret = new extDOMElement($name, $value, $this); // create the new
element with this Document as owner
return $ret;
}
}
class extDOMElement extends DOMElement {
function __construct($name, $value='', $owner=null,
$namespaceURI=null) {
if(!$owner instanceof extDOMDocument)
throw new DOMException(DOM_NOT_FOUND_ERR); // illegal owner
parent::__construct($name, $value, $namespaceURI);
$this->ownerDocument = $owner; //** this line causes a Fatal Error
}
// ... more class definition here
}
$doc = new extDOMDocument('test');
$el = $doc->createElement('tagname');
?>
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