[Lazarus] Some thoughts about the global 'Application' instance.

[Mattias Gaertner]

On Mon, 29 Jun 2009 16:24:47 +0200
Joost van der Sluis <joost at cnoc.nl> wrote:

> Op maandag 22-06-2009 om 00:39 uur [tijdzone +0200], schreef Mattias
> Gaertner:
> > On Sun, 21 Jun 2009 22:26:15 +0100
> > Martin Friebe <lazarus at mfriebe.de> wrote:
> > 
> > >[...]
> > > The beginning of this thread was, that 2 applications existed,
> > > because the developer was *forced* to included "interfaces":
> > > 
> > > Jost wrote in the initial mail of this thread:
> > > > I always thought that an application always had one
> > > > Application-instance from the TCustomAppliction class. But at
> > > > this moment this is not the case for fcl-web applications, or
> > > > daemon-applications which are using Lazarus-forms.
> > 
> > Whoever wants to continue this thread: Please give an example for a
> > fcl-web application or daemon-application which is using
> > Lazarus-forms.
> 
> Ow, that's easy: all those using WebModules and are streamed using the
> Lazarus-streaming system.

Webmodules are not lazarus forms (TForm/TFrame), are they?

 
> > > ....
> > > > But nowadays we are forced to include the 'interfaces' unit,
> > > > which uses the 'forms' unit which has it's own global
> > > > Application variable. So there are two TCustomApplication
> > > > descdendents initialized during the program!
> > > 
> > > Somehow the whole thread then picked up, the first half of this,
> > > and everyone started to discuss (at least this is the impression
> > > I got, apologies, if I overlooked anything) , how you could avoid
> > > having the application from the Forms unit, even if you use that
> > > unit (because apparently you have to). So the forms unit would
> > > have to detect the presence of another application....
> > 
> > And this is what I don't understand.
> > What part of unit "forms" is needed that does not require the
> > widgetset?
> 
> LResources. That's the only thing I need, nothing more. 

As Vincent wrote: LResources does not use unit forms (not even
indirectly). See the lcl/alllclunits.pp for units that do not use unit
forms.

 
> So actually only the Lazarus-streaming-mechanism is used. TWebModules
> are in fact TDataModules which you can use at design time to setup all
> kind of components. At run-time, those components are read from a
> resource and further nothing is needed.

TDataModule is part of unit classes, not of the LCL.

 
> But now with the new link-optimisation I'm forced to use the
> interfaces unit, and thus also the forms unit, which includes a
> widgetset, which I don't need. 

Indeed, you don't need it, so don't use it. You are not forced to use
forms nor interfaces.

> Using the nogui widgetset indeed solves this. 
>
> > > But all this only means work around the consequences, instead of 
> > > tackling the cause.
> > > 
> > > If I understand correctly, Interfaces now needs to be there,
> > > because of the smart-link - linker-alias trick used to reduce the
> > > exe size.
> > 
> > No. Unit interfaces was needed since the beginning. 
> > Before the change it was possible to avoid interfaces if:
> > - you use only constants and utility functions of the forms/controls
> >   unit.
> > - or if you use only the most basic things of TApplication, which
> >   already exist in TCustomApplication.
> 
> And when you only needed LResources. (And fileutil is also very
> usefull)

fileutil is independent of forms too. Again: see lcl/alllclunits.pp


> > Please give at least one good practical example before starting
> > theoretical discussions how to restructure the FCL/LCL.
> 
> Avoiding two Application-instances was only a side-effect of what my
> real intention was. 
> 
> The reason I started about a global CustomApplication in CustApp was
> that you can refer to the current Application-class, without knowing
> what type of application you are in.
> 
> For example: if you have a unit which is used in a daemon, web and
> Lazarus/GUI application you can call CustomApplication.HasOption() by
> just adding CustCgi to the uses.

Yes. That is useful.
But having two apps in parallel is not.

 
> I now think that I can add this without causing any problems for
> fcl-web/fcl-daemon/Lazarus and mseide if I just add a global variable
> in custapp:
> 
> var CustomApplication: TCustomApplication;

:)

 
> At first this will change nothing. But all frameworks which use the
> TCustomApplication-setup can set the global variable, so that it is
> accessible thoughout the whole program.
> 
> That way Lazarus/mseide/etc can choose how to use it (or not to use
> it)
> 
> But it would be nice if I could use LResources again, without using
> forms, but that's another story.

I hope this story has now happy ended. 

Mattias