subclassing bug?

RossDuncan · September 2005

I came across what seems to be a bug in Vanilla so I thought I'd mention it here to see what others think. I have a couple of fixes which may be useful to anyone with the same problem.

My extension wants to use a class which extends ApplyForm (from controls/apply.php). This won't work because extensions are loaded before the page controls file, so the superclass is not available, and we can't inherit from an undefined class. If I include() the controls file in my file, it is available for the subclass but then, when the page controls file is loaded, there is a "can't redefine class error". Catch 22.

The way I fix this is to change the method Page->Import so that it has include_once() once instead of include(). On its own this doesn't suffice because include_once() treats the file as different if it is included using absolute and relative paths (PHP bug?), so I need to change Page's constructor to replace


$this->ControlFile = "controls/".$this->Context->SelfUrl;

with


$this->ControlFile = agAPPLICATION_PATH . "controls/".$this->Context->SelfUrl;

Then it works.

It might be easier to change the init_* files to load the page controls before the extensions and avoid this whole palava, but I didn't try that.

RossDuncan · September 2005

There is another, sneakier, way to fix this, for those using php4 that don't want to modify their Vanilla files. I tell ObjectFactory to load a "trampoline" instead of the real class I want to use. The trampoline looks like this:


class MyApplyForm_TRAMP { 

var $file = "MyApplyForm.class.php";

function MyApplyForm_TRAMP(&$Context, $Param1 = "", ... , $Param10 = "") {
  include(sgOGI_PATH.$this->file);
  $this = $Context->ObjectFactory->NewContextObject($Context, "MyApplyForm",$Param1, ...., $Param10);
  }
}

The trampoline's constructor replaces itself with the class you really wanted. Because the text of MyApplyForm is read only when we try to instantiate the trampoline we avoid the problem of ApplyForm being undefined.

Sadly this behaviour is a parse error in php5, even with the compatibility mode turned on.

subclassing bug?

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