[fpc-pascal] Class Memory Table Size

[Daniël Mantione]

Op Tue, 8 May 2007, schreef Andrew Haines:

> Hi,
> =

> In this page
> http://www.freepascal.org/docs-html/prog/progsu139.html#x189-1950008.2.13
> in the VMT +0 is the "Size of object type data" and the same number in
> the negative is stored at +4. How important is it that this number is
> not changed after the object is created? I want to store a number
> especially at +0. What is stored after that does not matter.

These fields are used by several RTL routines that operate on classes, =

which will  no longer function correctly. For details we need to search =

the source code.

> The reason for this is, I want to trick gtk into thinking that a TObject
> is really a GObject. This is where the TypeID for GType's are stored. I
> know this won't work for most GObject's, but I am only implementing this
> for a GInterface which is looked up by the TypeID, so that is all I need.
> =

> I've tested this and it is working. But what horrible things can happen?

I think it is much better to use objects for this rather than classes. A =

construction like this:

type   gobject=3Dobject
         gobject_typeid:...;
       end;

       gobject_child=3Dobject(gobject)
         constructor init;
         destructor done;virtual;
       end;

... will exactly to what you want: the gobject_typeid is at offset =

0 while the size and vmt index are stored after that.

Dani=EBl