[fpc-devel] Adding procedures using nodes

[Sven Barth]

Am 04.08.2018 um 01:17 schrieb Ryan Joseph:
>
>> On Aug 2, 2018, at 2:41 PM, Ryan Joseph <ryan at thealchemistguild.com> wrote:
>>
>> So the way FreeInstance is called by adding it within a destructor isn’t exactly what I needed because it requires a destructor actually be present in the class.
>>
>> The next thing I’d like to try is adding a procedure dynamically using nodes. I’ve seen how if statements are made doing things like:
> Once again I think this is not useful so it can be disregarded.
>
> I wanted to learn how I could call Free on class fields (like management operators call Finalize on records) but it’s more complicated than I thought (again). Records with management operators hook into the RTTI system it looks like, but how does a record with management operators get added to the classes RTTI information? I mean in TObject.CleanupInstance there is a vInitTable which gets set if the record has management operators in them but I can’t find where.
The whole VMT including vInitTable is generated by the compiler in 
ncgvmt. Take this example:

=== code begin ===

program thelloworld;

{$mode objfpc}
{$modeswitch advancedrecords}

type
   TTestRec = record
     f: LongInt;
     class operator Initialize(var aRec: TTestRec);
   end;

   TTest = class
     fRec: TTestRec;
   end;

class operator TTestRec.Initialize(var aRec: TTestRec);
begin
end;

var
   t: TTest;
begin
   t := TTest.Create;
end.

=== code end ===

If you compile this with -al you'll see the following symbols in the 
assembly code:

VMT_$P$THELLOWORLD_$$_TTEST: The VMT of the TTest class (look at 
rtl/inc/objpash.inc for the type TVmt to see how a VMT is structured)
INIT_$P$THELLOWORLD_$$_TTEST: The init table of the TTest class 
(referenced from the VMT)
INIT_$P$THELLOWORLD_$$_TTESTREC: The init table of the TTestRec record 
(referenced from TTest's init table using an indirect reference)

Regards,
Sven