[fpc-pascal] Design Patterns Questions

[Michael Van Canneyt]

On Sun, 28 Oct 2012, bsquared wrote:

> Hi all,
>
> It has been some time since I have used FPC/Laz.  I was looking for some
> information on 'observer pattern' the other day, and I found this
> article[1].  I notice that it is a bit old, and it makes me question
> whether or not I have made an error following it.
>
> I get an invalid cast error at this code
>   (DigitalClock1 as ISubject).Attach(fClockTimer as IObserver);
> which is actually flipped and should be
>   (fClockTimer as ISubject).Attach(DigitalClock1 as IObserver);
>
> So, my questions ...
>  Is the article out of date?
>  Are these patterns implemented in the base code?

The observer pattern is implemented in tiOPF.

>  And as an aside, what is the state of tiOPF, I could not get it to
>  install in Lazarus 1.02.

Version 3 is designed to work with Delphi 2009 and higher.
Graeme Geldenhuys actively maintains tiOPF version 2. 
It works definitely with Lazars 1.0.2, I use it myself.

Michael.