Hi,

Below is part of the Interfaces documentation. I disagree with the documentation mentioned below.

================================
Interfaces - section 7.1
http://lazarus-ccr.sourceforge.net/fpcdoc/ref/refse34.html#x77-850007.1

"There are no visibility specifiers. All members are public (indeed, it would make little sense to make them private or protected)." ================================

Maybe it is just Joanna Carter and myself that disagree with this statement. But here goes... Joanna and I both agree that Interfaces when implemented in classes should rather be made private or protected instead of public.

The reason is simple. You are supposed to (or preferred to) access the methods via a Interface from another object instance and not the object instance itself - in which case, even if the methods are private or protected you will still have access to them via the Interface. Also the object who implements the Interface will be able to access the methods either way. But from another object instance - it is always preferred to access those methods via a Interface.

Example:

var
   lFilter: ItiFiltered;
   lCriteria: TtiCriteria;
begin
   lCriteria := nil;
   if Supports(Visited, ItiFiltered, lFilter) then
   begin
     if lFilter.HasCriteria then
       lCriteria := lFilter.GetCriteria;
   end;
...
end;

It might be worth mentioning this, instead of simply saying that there is no point in having the Interface methods implemented as private or protected. Also it (Borland docs) does say that there are no visibility specifiers, but where does it say they are Public by default? That is just wrong.

Regards,
- Graeme -

This is about visibility of the methods/properties of the interface itself. Do not confuse it with visibility of interface methods in implementor object, where usual visibility rules (described elsewhere) apply.

Indeed, in the implementors it makes certain sense to reduce visibility of interface methods, so they can be called only via interface and not via object instance. But this is more related to the design of particular application/library, than to the language specification.

Regards,
Sergei

True, but from the comment in brackets I deduced that it was a reference to when they (Interfaces) get implemented. Either way, then maybe a comment needs to be added that Interfaces having no visibility specifiers when the interface is declared, does NOT mean they they must also be Public visible when implemented in a class.

I feel the wrong message is being sent in that documentation.

Regards,
- Graeme -

You are misinterpreting the statement. The statement is that IN THE INTERFACE DECLARATION, all the members are public.

No assumption is made about the visibility of the methods in the class that actually implements the interface.

Michael.

I will add a comment as you suggest. The documentation is meant to enlighten the user, not confuse him :-)

Michael.

Michael Van Canneyt wrote

I will add a comment as you suggest. The documentation is meant to enlighten the user, not confuse him :-)

:-) Thanks Michael.

Regards,
- Graeme -