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
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