Am 08.05.2021 um 19:38 schrieb Ryan Joseph via fpc-devel:
On May 8, 2021, at 11:18 AM, Sven Barth <pascaldra...@googlemail.com> wrote:
It's not about reference counted classes vs. managed records, but about whether
it's *per type* or *per variable*, the implementation details are completely
irrelevant for now.
So the biggest concern you see if that classes are easier to assign to
non-reference counted classes? The only difference between classes and records
in this regard is that records give errors unless you assign directly to the
same record type, where classes can be assigned to super-classes which may not
be managed.
As you say there would need to be at least a warning if you cast a managed
class to another class type or make it forbidden completely. I don't see that
as a deal breaker personally but you seem to feel pretty strongly about it.
It seems that you don't work much with classes then. If one disallows
the assignment of a reference counted class to a non-reference counted
one then you can't use e.g. TStringList.Objects. There is also the
problem of method pointers, which essentially only have a Pointer as
Self data. Also a reference might escape in a parent class (for this
example I'll use the syntax I used in my branch):
=== code begin ===
{$mode objfpc}
type
TTest = class
protected
procedure DoSomething;
end;
TTestSub = class refcounted(TTest)
public
procedure Test;
end;
procedure TTest.DoSomething;
begin
// maybe this functions stores the reference
SomeFuncThatTakesAObject(Self);
end;
procedure TTest.Test;
begin
DoSomething;
end;
=== code end ===
Obviously these problems won't be solved with the alternative approach
either, but likely one can make clear more easily that the use case is
for local instances.
Anyways I wrote up a little wiki with some potential implementation notes about a default
property (which overlaps on the "defaults implements" as traits stuff). Important
points are restricting what types can be default properties (classes and maybe/probably
typed pointers) and limiting hoisting to subscripting, so it's kind of like the ->
operator overload in C++.
https://github.com/genericptr/freepascal/wiki/Default-property
It shouldn't hoist only public members, it should hoist according to the
visibility rules (thus the hoisting depends on the callsite), otherwise
it won't behave like Pascal classes do and thus we can forget it right away.
Regards,
Sven
_______________________________________________
fpc-devel maillist - fpc-devel@lists.freepascal.org
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
