fpc/compiler/new/symtable/xobjects.pas
daniel 59cfa402c9 * Ported hcgdata to new symtable.
* Alignment code changed as suggested by Peter
  + Usage of my is operator replacement, is_object
2000-03-11 21:11:24 +00:00

81 lines
2.2 KiB
ObjectPascal

unit xobjects;
{
$Id$
Copyright (c) 2000 by Daniel Mantione
member of the Free Pascal development team
This unit provides an extends the Tobject type with additional methods
to check the type of an object. It should only be used within
Turbo Pascal, the Free Pascal objects unit already contains this
functionality.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
****************************************************************************
}
interface
{As TP does not store a link to the parent's VMT in the VMT, a function like
is_object would be impossible.
We use a very dirty trick to get it done; in an objects constructor the
setparent procedure should be called, which stores the link to the parent
into the DMT link. (!!!)}
uses objects;
type Pobject=^Tobject;
Tobject=object(objects.Tobject)
function is_object(typ:pointer):boolean;
procedure setparent(typ:pointer);
end;
implementation
type vmt=record
size,negsize:word;
dmtlink:pointer;
end;
function Tobject.is_object(typ:pointer):boolean;assembler;
asm
les di,self
mov bx,[es:di] {Get vmt link.}
jmp @a3
@a2:
mov bx,[bx+4] {Get dmt link, offset.}
or bx,bx
mov al,0
jz @a1
@a3:
cmp bx,typ.word {Compare with typ.}
jne @a2
mov al,1
@a1:
end;
procedure Tobject.setparent(typ:pointer);assembler;
asm
les di,self
mov bx,[es:di] {Get vmt link.}
mov ax,typ.word
mov cx,typ+2.word
mov [bx+4],ax
mov [bx+6],cx
end;
end.