[Newbies] Re: Alternative for static const...

[Greg Trasuk]

I suspect you are "thinking in Java".  Indeed, when you run a Java
program, its class variables will be initialized when the class is
loaded into the virtual machine, in other words the first time you
reference the class.

But Squeak is different; it's a live image system.  When you are editing
the class, you're actually making changes to the class in the running
system.  When you restart Squeak, the entire memory image of the virtual
machine is reloaded from the last saved image, including the state of
any class variables (and instance variables, and processes, etc).

Cheers,

Greg.

On Tue, 2007-02-27 at 07:51, Mispunt wrote:
> I am sorry, I did mean execute. I hoped that it would execute
> initialize when the class (or variableNames) where called by the
> program..
> After running/execute the initialize method it is working :)
> 
> Thanks for you'r help,
> 
> Mispunt
> 
> On 2/27/07, Bert Freudenberg <bert at freudenbergs.de> wrote:
> > What do you mean with "isn't running"? As I wrote, you have to
> > execute it manually whenever you change the initialize method.
> >
> > - Bert -
> >
> > On Feb 27, 2007, at 13:33 , Mispunt wrote:
> >
> > > After some better testing, It doesn't work :S It seems that the
> > > initialize of the constants class isn't running... (the normal
> > > classVariableNames are working...) I have to use the poolDictionary
> > > because there are some codes that return in a lot of classes..
> > >
> > > Mispunt
> > >
> > > On 2/27/07, Mispunt <mispunt at users.sourceforge.net> wrote:
> > >> Thanks Bert, it works. When I am using the poolDictionary it isn't
> > >> possible to use the constants in the Workspace right? or do I have to
> > >> write methods for them when I want to use them? (well I don't want
> > >> to,
> > >> because it is just for testing purpose).
> > >>
> > >> Mispunt.
> > >>
> > >> On 2/27/07, Bert Freudenberg <bert at freudenbergs.de> wrote:
> > >> > On Feb 27, 2007, at 10:08 , Mispunt wrote:
> > >> >
> > >> > > Hi all,
> > >> > >
> > >> > > For programming my Lego Mindstorms NXT I have to use codes
> > >> like 16r1F.
> > >> > > But I actually want to be able to use "readable" codes. In a
> > >> language
> > >> > > like Java I will do that with a static const, but as far as I
> > >> know I
> > >> > > have to do it with symbols in Smalltalk.
> > >> >
> > >> > No, there is a better way.
> > >> >
> > >> > If you are inside one class (or its subclasses), you would use
> > >> "class
> > >> > variables", one per constant. You add them in the class template:
> > >> >
> > >> > Object subclass: #Bla
> > >> >         instanceVariableNames: ''
> > >> >         classVariableNames: 'Const1 Const2'
> > >> >         poolDictionaries: ''
> > >> >         category: 'Bert-Bla'
> > >> >
> > >> > and the initialization code is in a class-side #initialize method:
> > >> >
> > >> > initialize
> > >> >         "self initialize"
> > >> >         Const1 := 16r1F.
> > >> >         Const2 := 12345.
> > >> >
> > >> > You need to execute the "self initialize" in the browser to do the
> > >> > initialization. It will be executed automatically when loaded into
> > >> > another image.
> > >> >
> > >> > Class variables are capitalized because they are sort-of "global",
> > >> > they can be used in the defining class, its metaclass, and all
> > >> their
> > >> > subclasses. If you need to give access to these variables across
> > >> the
> > >> > class hierarchies, then you would do the same, but as a subclass of
> > >> > SharedPool:
> > >> >
> > >> > SharedPool subclass: #BlaConstants
> > >> >         instanceVariableNames: ''
> > >> >         classVariableNames: 'Const1 Const2'
> > >> >         poolDictionaries: ''
> > >> >         category: 'Bert-Bla'.
> > >> >
> > >> > To use this "pool" of variables in another class, list it as a
> > >> "pool
> > >> > dictionary":
> > >> >
> > >> > Object subclass: #Bla
> > >> >         instanceVariableNames: ''
> > >> >         classVariableNames: ''
> > >> >         poolDictionaries: 'BlaConstants'
> > >> >         category: 'Bert-Bla'
> > >> >
> > >> > This makes all class variables of BlaConstants available to Bla
> > >> as if
> > >> > they were class variables.
> > >> >
> > >> > There are quite a few other ways to allow "global" variables in
> > >> > Smalltalk, but this one is the "clean" way to do it which works
> > >> > nicely with tools like Monticello.
> > >> >
> > >> > - Bert -
> > >> >
> >
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