[Openmcl-devel] something is not quite right in cocoa land
alexcrain at mail.widgetworks.com
Fri Jun 10 15:41:37 EDT 2005
On Jun 8, 2005, at 11:13 PM, Gary Byers wrote:
> If the class involved is declared, the current mechanism is about the
> same as the old mechanism: we have search trees which contain all
> known (declared) ObjC classes and metaclasses; for a given pointer:
> 1) if the pointer is found in the metaclass tree, it's that
> 2) if the pointer is found in the class tree, it's that class
> 3) if we think that it's safe to indirect through the first word in
> the pointer (the "isa" field) and that first word is found in the
> class tree, the pointer is an instance of that class.
> This mostly happens in the function RECOGNIZE-OBJC-OBJECT.
> When we start up/restart a saved images, we enumerate all foreign
> classes. (We should also ensure that this happens whenever someone
> loads an auxiliary ObjC library.)
> If the class is declared, it gets added to the search trees; this is
> how things have worked for a long time.
> If the class is undeclared, it gets added to another search tree
> (one used to track "private ObjC classes"; I don't remember its name
> offhand.) The datum associated with each class in the private class
> tree is a little structure that's supposed to contain information
> about the nearest declared superclass. That information isn't
> filled out yet; the code that enumerates all classes should make
> a pass over the private class tree and fill in that information.
> Once that information's available, case 3 above gets extended;
> 3b) if the pointer's "isa" field is found in the private class
> tree, the pointer is an instance of the public class associated
> with that private class. We may or may not want to define some
> extra pointer type bits so that we can recognize that the
> isn't a "true" or "direct" instance, but I think that we can
> almost always ignore this distinction.
So if I'm tracking this right, an undeclared objc class is not an
instance of a class
but rather and instance of PRIVATE-OBJC-CLASS-INFO. This isn't a problem
because the only thing that need to understand undeclared classes
SEND, %SEND, PRINT-OBJECT and a few assorted things that call OBJC-
CLASS-OF and TYPE-OF are going to need to return the nearest declared
in order to be consistent but that seems reasonable enough since any
an undeclared type are effectively private.
There are several places in the code where we can safely assume that
a macptr is
a objc instance or class: methods that return :ID and ALLOCATE-
INSTANCE come to mind.
If we insert code in the method returns that will register objects on
the fly then we should
catch all the cases.
Did I miss anything?
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