Re: [Vala] [Genie] Object members

[Patrick Castle <lemeia bigpond com>]

Jamie McCracken wrote:
> On Wed, 2009-10-28 at 10:39 +0000, Patrick Castle wrote:
>   
> > Just stuffing about at the moment getting my head about creating classes in
> > Genie. From what I gather, every variable you declare outside of a method is a
> > member/property of that class.
> >
> > What I'm finding a bit confusing is there isn't just one way to declare a
> > property it seems - but both ways don't work consistently.
> >
> > For example, I have class "Test" and I want it to have a private property "a"
> > not accessible to external callers. It seems like these are the options:
> >
> > class Test : Object
> >     _a : int
> >
> > or
> >
> > class Test : Object
> >     prop private a : int
> >
> > or
> >
> > class Test : Object
> >     prop _a : int
> >
> > but not
> >
> > class Test : Object
> >     private a : int
> >
> >     
>
>
> a : private int
>
>
>   
> > My first question - is there any reason why that last one shouldn't compile?
> > Also - why actually have so many ways to declare the same thing? Is it
> > deliberate or just an accident of the syntax checking? 
> >     
>
> they are not all the same
>
>
>
>   
> > Also - does Genie have the concept of a class variable, or are they all just
> > instance variables? My initial temptation was to use static in the declaration
> >
> > class Test : Object
> >     prop static a : int
> >
> > This actually starts spitting out all sorts of errors when compiling the C
> > source, so perhaps it gets further than it should. Is it an illegal declaration?
> > And if so, should it be caught before it gets as far as the C source being
> > created and compiled?
> >
> > On the Genie homepage it says:
> > All methods, properties and events can also take modifiers to define further
> > options.
> >
> > I assumed that would mean that all modifiers were legal. So I thought I should
> > try the other modifiers.
> >
> > abstract:
> >
> > class Test : Object
> >     prop abstract a : int
> >
> > This one compiles OK, but if you create an instance of the class and assign a
> > value to the property you get a Segmentation Fault when you run it. 
> >     
>
> possibly a bug - im not sure if abstract properties are supported
>
>   
> > I looked at the definition of abstract and it seems to say that it should not be
> > defined in the class in which it's declared but only in the subclass. So I
> > created a subclass and defined it there instead and I still get a clean compile
> > but a Segmentation Fault when running.
> >
> > I'm guessing that this is only meant for methods rather than properties - but if
> > so, it would probably be a good idea to make a distinction on the web page
> > between method modifiers and property modifiers. Seems like the remaining
> > modifiers look relevant only to methods as well.
> >
> > Also - I think rather than getting a Segmentation Fault, improper use of these
> > modifiers should probably throw exceptions during the compile.
> >  
> > So to summarise, declaration of properties implies public access unless keyword
> > private is used (or underscore). Your options are: _var, prop private var, prop
> > _var.
> >     
>
> if you dont use prop then its a field 
>
>   
> > There is no such thing as a class variable in Genie.
> >     
>
> not sure what you mean here?
>
>   
> > Would that be an accurate summary?
> >     
>
> no
>
>   
> > Regards
> > Patrick
> >
> > _______________________________________________
> > Vala-list mailing list
> > Vala-list gnome org
> > http://mail.gnome.org/mailman/listinfo/vala-list
> >     
Thanks for that. I looked back at the Genie page and did a bit of Googling. I think I understand the 
distinction between field and property. It would seem from a good practice point of view that fields would 
generally be private and properties would generally be public. Would that be a reasonable way to explain it? 
If so - I understand where I would want to use one or the other.

It looks like if I'd come from a C# or Vala background this distinction would have been obvious from the 
start, so apologies for going down the wrong track.

a : private int (DOH! Didn't try it that way - embarrassed now)

Regards
Patrick