Preference Pragmas in instance methods?

Nicolas asked me to move the #traceMessages preference to
SystemNavigation and implement it as a pragma.

SystemNavigation is a Singleton, therefore the SystemNavigation
#default instance uses instance-side methods to, for example, define
its 'browserClass' and 'hierarchyBrowserClass'.

After trying to add #traceMessages there, I quickly discovered that
Preference pragmas were intended only to be for class-side methods.
Noting in Preferences class>>#prefEvent:, it sets up the
SystemChangeNotifier to only worry about classes that are #isMeta.

I could refine that #isMeta guard to allow singletons, although to do
that I'd want to introduce a Singleton class and move SystemNav
there...

Another thing we could do is remove the guard; if someone puts a
preference pragma in an inst-method, any problem with that?

Of course, we could just keep it as a standard old preference..

Anyone have any preferences?  :)

2010/3/7 Chris Muller <[hidden email]>:
> Nicolas asked me to move the #traceMessages preference to
> SystemNavigation and implement it as a pragma.
>

I would say suggested...

What an instance side preference would mean ?
A different preference for every instance ?
My opinion is that they belong to class only.

Nicolas

> What an instance side preference would mean ?
> A different preference for every instance ?

There is only one instance of SystemNavigation.

> My opinion is that they belong to class only.

I suppose I could add the first class-var to SystemNavigation.
However, SystemNavigation is a Singleton _instance_ which is where its
other state and API are.  So we would have this lone #traceMessages
option on the SystemNavigation class-side just so we could use a
pragma.  It creates a dichotomy about which SystemNavigation is
supposed to be used.  Since you were only suggesting anyway, the
easiest thing for now would probably be to just leave it in
Preferences.

 - Chris

On 3/7/2010 5:04 PM, Chris Muller wrote:
>> What an instance side preference would mean ?
>> A different preference for every instance ?
>
> There is only one instance of SystemNavigation.
>
>> My opinion is that they belong to class only.
>
> I suppose I could add the first class-var to SystemNavigation.

You don't have to. You can delegate the class-side method to the
singleton instance, i.e.,

SystemNavigation>>traceMessages
        "Accessor for preference"
        <preference: ....>
        ^self default traceMessages

etc. This requires the methods on the class but not the state.

Cheers,
   - Andreas