Hi,

the reference manual is not explicitly clear in describing class declarations. Is it true for classes as for objects that the first block of components after the class header are visible as if declared public?

E.g.

TAnyClass = class
	fField:anytype;
end;

would make fField visible "public"?

And one other question:
Does object pascal allow a class declaration marked as an abstract class? Like in java for making sure the class can never be instantiated itself, only it's descendants can be?

Smth. like:

TAnyClass = abstract class(...)
...
end;

TIA,
Marc

It would be "published".

AFAIK, not.

Vincent

Marc Santhoff wrote

Does object pascal allow a class declaration marked as an abstract class? Like in java for making sure the class can never be instantiated itself, only it's descendants can be?

The compiler will issue a warning if you instantiate a class with abstract methods

Only if creating an instance straight from the class, eg:

This will warn:

begin
   VMyObj := TMyAbstract.Create;

This wont:

var
   VMyClass: TMyAbstractClass;
begin
   VMyClass := TMyAbstract;
   VMyObj := VMyClass.Create;

iirc only if the class or a superclass is declared with $M+

Classes with RTTI information use published, otherwise public. See the {$M+} switch, for example TPersistent.

No.
Just add abstract methods and you will get compiler warnings when instantiating such a class.

Mattias

Correct. The compiler can only warn about compile time errors, not runtime errors.
For runtime you can use

constructor TMyAbstract.Create;
begin
  if ClassType=TMyAbstract then raise Exception.Create('abstract
class');
  inherited Create;
end;

Mattias

Very nice, exactly what I need in the situation right now. Although a compiler switch for telling fpc to bark and stop on error when instantiating abtract classes would be nice I can live with this solution very well. :)

Thanks for this one and to anyone helping,
Marc