Thanx for the explanation rob. I'll definitely have a look at it!
from Robert Meek dba Tangentals Design -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rob Kennedy Sent: Tuesday, January 10, 2006 2:16 PM To: Borland's Delphi Discussion List Subject: [SPAM]Re: Class helpers and StringList alternatives Robert Meek wrote: > Also that's interesting about TObject. Has it been that way since > version 1? Of course not. Before version 8, there was no other class for TObjectHelper to help. Class helpers were introduced so that Borland could tack the old TClass and TObject methods that we're used to onto .Net's System.Object without having to write a completely separate class hierarchy. The .Net class is missing several methods that Delphi programs use, especially ClassName, Dispatch, and Free. Delphi's TClass is sort of like System.Type, but not quite. TObject is sort of like System.Object, but not quite. Class helpers aim to bridge the gap. Class helpers cannot include any instance variables. They can only contain methods and class variables. This is because the class helper does not get instanciated with the original class. TObjectHelper.Free could have been written as a standalone function, if .Net supported such a thing. It would look like this: procedure Free(Self: TObject); begin if Assigned(Self) and (Self is IDisposable) then begin // etc. end; end; But that makes it inconvenient to call since the scope of Free is no longer related to the scope of TObject. Internally, a class helper is a class of its own. Whereas we usually think of a method of a normal class having a "hidden" Self parameter, class-helper classes actually have an explicit Self parameter added to whatever parameters were declared in the source code. If you look at TObjectHelper.Free in Reflector, you'll see that it's declared something like this: procedure TObjectHelper.Free(Self: System.Object); The class-helper instance never operates on itself. Instead, it operates on the instance of the related class. Delphi doesn't provide any language support for class helpers in Win32, but it's possible to write classes that do the same task. The technique is described in one of the newsgroup articles in the search I mentioned yesterday. > I was under the assumption that this was something new but maybe > not. As I've never even looked at the code for that class I think now would > be a good time for me to check it out! To get a better idea of what you're looking at, be sure to compare the .Net code with the Win32 version. -- Rob _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi
