On Mon, 16 Jan 2023, Wayne Sherman via fpc-devel wrote:
On Mon, Jan 16, 2023 at 12:16 PM Wayne Sherman wrote:
I need clarification about the auto generated class index
specifiers. Do they always start at 0 in each descendant
class, or are they unique across all descendant classes?
TBaseObject --> TChild --> TGrandChild
TChild = class(TBaseObject)
...
published
property Field1: string index 0...
property Field2: string index 8...
end;
TGrandChild = class(TChild)
...
published
property Field3: string index 16... // does this continue at 16
or start at 0 again?
property Field4: string index 24...
end;
It appears the index specifiers restart at 0 in each descendant class.
Which is why this code works:
procedure TBaseObject.MarkPropertyChanged(AIndex: Integer);
begin
If Assigned(FBits) then
FBits.SetOn(GetParentPropCount+(AIndex shr IndexShift));
end;
Yes. The reason is the code generator:
Ideally, every property simply has a unique index specifier.
But when generating classes, the code generator has no way of knowing how
many properties exist in parent classes, so it must start at 0.
(
one could imagine helping the code generator by specifying a start point
per class:
1000
2000
3000
etc.
)
function TBaseObject.IsPropertyModified(Info: PPropInfo): Boolean;
begin
Result:=Not Assigned(FBits) or FBits.Bits[Info^.NameIndex]
end;
The name list (from which NameIndex gets its value) includes the
published property names of all the parents plus the names in the
current class, so for a REST property in a descendant class with Index
specifiers starting at 0:
GetParentPropCount+(IndexSpecifier shr IndexShift) = NameIndex
Yes.
This was long ago, but I seem to remember that I changed that code in production,
so it would use the same mechanism as MarkPropertyChanged, because there were
published properties not part of the REST scheme, and in that case, the equation does
not hold true (becasue nameindex includes non-REST properties).
That change does not seem to have made it in FPC.
Michael.
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