Re: [Vala] Understanding object creation (and other things)

["Alexandre Moreira" <alexandream gmail com>]

On 4/22/07, Jürg Billeter <j bitron ch> wrote:
> On Son, 2007-04-22 at 11:55 +0100, Phil Housley wrote:
> > > You can do this with construct-only properties without storing the value
> > > anywhere.
> > ...
> > > The construct in the parameter of the creation method is just a short
> > > version of setting the property x to the value of the argument x.
> >
> > Ok, I think I'm getting some of this.  To add a little complexity
> > though, say I want to do something like a multiplier that stores the
> > answer and not the terms.  This means I need two construct parameters
> > to set one value:
> >
> > class Mul {
> >       private int answer;
> >
> >       public int get_answer() {
> >               return answer;
> >       }
> >
> >       public void set_terms(int x, int y) {
> >               answer = x * y;
> >       }
> >
> >       public Mul(int x, int y) {
> >               set_terms(x, y)
> >       }
> > }
> >
> > The closest I can get in vala seems to be:
> >
> > [...]
> >
> > But that keeps the original x and y around for ever, even when the
> > terms have been changed.  And is a lot of work also.
> >
> > Is there a way of cutting this back now, or is the syntax likely to
> > shrink in the future maybe?
>
> The only sensible possibility to make this simpler would be to allow
> accessing the construction parameters in the constructor, maybe
> something like that:
>
> class Mul {
>         private int answer;
>
>         public int get_answer() {
>                 return answer;
>         }
>
>         public void set_terms(int x, int y) {
>                 answer = x * y;
>         }
>
>         public Mul(construct int x, construct int y) {
>         }
>
>         // implicitly declare construct-only parameters x and y
>         // with a default value of -1
>         construct (int x = -1, int y = -1) {
>                 set_terms(x, y)
>         }
> }
>
> Would something like that make sense?
>
> The way I'd implement such a class currently is by using a helper method
> for construction - assuming that you don't want to create instances of
> subtypes in the same manner.
>
> class Mul {
>         private int answer;
>
>         public int get_answer() {
>                 return answer;
>         }
>
>         public void set_terms(int x, int y) {
>                 answer = x * y;
>         }
>
>         public static Mul! create_with_terms (int x, int y) {
>                 var mul = new Mul ();
>                 mul.set_terms (x, y);
>                 return mul;
>         }
> }

A little bit off-topic but. What is it with those '!' on type
references ? What do they mean ?

Thanks,
Alexandre Moreira.

> Jürg
>
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