> On May 7, 2021, at 2:52 PM, Sven Barth <pascaldra...@googlemail.com> wrote:
> As said the main problem of reference counting on object instances, 
> especially if enabled by default like the Delphi NextGen compiler did, will 
> lead to problems in *existing* code and thus is a no-go. 

What did you think about me other email that had ideas to add compiler 
directives like $M+? The way record management operators are implemented is 
that if you include any of the operators then the type becomes "managed" in the 
same way other ref counted types are handled.

For classes this is different because there is a hierarchy which is now altered 
but the compiler could still insert a hidden super class above it and use that 
to store the extra data. Indeed this would mean that existing classes (like the 
RTL) would not be eligible for reference counting unless it was compiled using 
said directive.

For example the follow class:

 TMyObject = class(TBaseClass)

would become:

 TMyObject_RefCounted = class abstract(TBaseClass)
  strict private
    refCount: LongInt;
 TMyObject = class(TMyObject_RefCounted)

and now "TMyObject" is a managed type and Initialize/Finalize/AddRef/Copy will 
be called. It occurs to me now though that the ref counting would be tied to 
the type so if you cast the class to TObject and passed it around then ref 
counting wouldn't happen. Not sure if that's a deal breaker or not but it could 
easily cause hard to fix memory leaks.... just like normal classes. :)

        Ryan Joseph

fpc-devel maillist  -  fpc-devel@lists.freepascal.org

Reply via email to