[fpc-pascal] Get TMethod from function reference

[Sven Barth]

Am 16.09.2022 um 03:53 schrieb Hairy Pixels:
>
>> On Sep 11, 2022, at 3:28 PM, Ondrej Pokorny via fpc-pascal <fpc-pascal at lists.freepascal.org> wrote:
>>
>> You should be able to get the Invoke procedure pointer from the RTTI.
> Sorry Sven mentioned this I must have glossed over it. So yes I am storing the function reference in a class so it’s not going to get freed.
>
> Given this example here can you explain how to get the procedure pointer from the RTTI? Even so if you get the procedure pointer you need the class instance also, which reference must be keeping somewhere right?
>
> type
>    TProc = reference to procedure;
>    TMyClass = class
>      procedure DoThis;
>    end;
>
> var
>    p: TProc;
>    c: TMyClass;
> begin
>    c := TMyClass.Create;
>    p := c.DoThis;
>    // Can I get the refefence to "c" back using the RTTI?
> end.
>

No, you can't get a reference to c, because the compiler will 
essentially create the following code:

=== code begin ===

type
   TProc = reference to procedure;
   TMyClass = class
     procedure DoThis;
   end;

   TCapturer = class(TInterfacedObject, TProc)
     m: procedure of object;
     procedure Anonymous1;

     procedure TProc.Invoke = Anonymous1;
   end;

var
   p: TProc;
   c: TMyClass;
   capturer: TCapturer;
   capturer_keepalive: IUnknown;
begin
   capturer := TCapturer.Create;
   capturer_keepalive := capturer;
   c := TMyClass.Create;
   capturer.m := @c.DoThis;
   p := capturer as TProc;
end.

=== code end ===

Regards,
Sven