Hello FPC-Pascal,

If I have a class like:

TMyClassPublished=class(TObject)
published
  procedure MyProcedure; virtual;
end;

And a derived one:

TMyClassDerived=class(TMyClassPublished)
public
  procedure MyProcedure; override;
end;

Is there any difference in the derived one with less visibility in the method ? This means, does it use less/more memory, more/less calling speed, more/less RTTI information, ... ?

Thank you.

no, no, no, no

You cannot lower visibility, since the following example is still possible:

var
   a:TMyClassPublished;
begin
   a := TMyClassDerived.Create;
   a.MyProcedure;
end;

it will use the scope of a and not the "redefined" scope in TMyClassDerived

Marc

Hello FPC-Pascal,

MW> no, no, no, no
MW> You cannot lower visibility, since the following example is still possible: MW> var
MW> a:TMyClassPublished;
MW> begin
MW> a := TMyClassDerived.Create;
MW> a.MyProcedure;
MW> end;
MW> it will use the scope of a and not the "redefined" scope in TMyClassDerived

That was exactly my suspect, but as RTTI was in the game, maybe some differences happend.

I had found this "visibility lower" warnings all along the LCLfpgui interface, so I think I will move them to the expected "published" level as parent TWSxxx classes.

What useful for put procedure in Publish?

Hello FPC-Pascal,

Friday, April 16, 2010, 8:42:32 AM, you wrote:

ZD> What useful for put procedure in Publish?

I do not know :-? I'll ask in the Lazarus list.

Published methods can be found with TObject.MethodAddress, that's how the lfm hook event handlers (and why Form event handlers are published).

Best regards,
Flávio

Hello FPC-Pascal,

Friday, April 16, 2010, 9:06:45 PM, you wrote:

FE> Published methods can be found with TObject.MethodAddress, that's how FE> the lfm hook event handlers (and why Form event handlers are FE> published).

Yes, but thats for streamable objects like TForm, or any component, but I think that that's not the case of TWSxxxx objects which are the widgetset interface, and also all of them are "class procedure".

Marc says in Lazarus that a "virtual class tree" is formed with such published methods, I do not know the need of it or the mission, but if it is OK it is OK ;) for me.

Sure, I was just saying that in a different context. I found Marc's observation very weird, and I'm (still) going to check it.

Flávio

Its not my observation, but my implementations :)

Imagine the following "base" widgetdset tree (best viewed with a fixed font)

TWSBase
|
+ TWSWinControl
| |
| + TWSButton
|
+ TWSSomeOther

Now we have a widgetset, say XXX, implementing these classes

when you use the normal inheritence you get a tree like:

TWSBase - TWSXXXBase
|
+ TWSWinControl - TWSXXXWinControl
| |
| + TWSButton - TWSXXXButton
|
+ TWSSomeOther - TWSXXXSomeOther

Now you see a problem here. You would expect TWSXXXButton to be derived from TWSXXXWinControl, but it isn't, so it doesn't have the TWSXXXWinControl implementation.

Now comes the "vitrual" class tree lazarus uses. Based on RTTI it creates its own VMT tables, rewriting the tree to:

TWSBase
|
+ TWSXXXBase
|
+ TWSWinControl
| |
| + TWSXXXWinControl
| |
| + TWSButton
| |
| + TWSXXXButton
|
+ TWSSomeOther
|
+ TWSXXXSomeOther

Now TWSXXXButton is derived from TWSXXXWinControl

Marc

Interesting.....

I thought (not even sure why I thought it, or were I pcked it up; so it may be wrong, in which case just tell me)...
... that the compiler could optimize an "inherited" call.

TBase = class
   procedure Foo; virtual;
end
TChild= class
   procedure Foo; override;
end

Now if I call "BaseVariable.Foo" from anywhere, it needs to find Foo in the VMT, because the actual object could be of either class.

BUT

procedure TChild.Foo;
begin
   inherited;  // or:  inerithed Foo;
   // do more
end;

I thought that in this last case, the compiler would know, that inherited points to TBase.Foo; and the compiler would optimize the code, to call directly (skipping the VMT) ?

But I guess I am wrong about that? OR how else could the above work?

Martin

2010/4/17 Flávio Etrusco :

Yes it is useful info for me,
Is that mean descending from TForm (or any class) without mentioned "published" or any of (public, protected, private) it will be considered as published?

Thanks

Yes. If you want less published use the TCustomXXX, e.g. TCustomForm.

Mattias

I meant

If i use, if i not mentioned "published"

TMyForm= class(TForm)
   procedure Method1;
end;

is is equal to

TMyForm= class(TForm)
published
   procedure Method1;
end;

Thanks in advance

Yes, because TForm descends from TPersistent.
Normal classes have "private" as default visibility.

Mattias

Your correct, thats why toyu are not allowed to use inherited in these
classes, but
   procedure TChild.Foo;
   begin
     TBaseClass(ClassParent).Foo;
     // do more
   end;

Marc