Re: [Vala] Ownership syntax changes

[Yu Feng <rainwoodman gmail com>]

On Sat, 2008-12-20 at 23:57 +0100, Hans Vercammen wrote:
> On Sat, 2008-12-20 at 08:24 +0100, Jürg Billeter wrote:
> > On Sat, 2008-12-20 at 02:19 +0100, Hans Vercammen wrote:
> > > On Fri, 2008-12-19 at 12:10 +0100, Jürg Billeter wrote:
> > > >       * `(owned)' cast replaces `#' reference transfer expression
> > > >
> > > > Even less used, equally unintuitive. Example of new syntax:
> > > >
> > > > string foo = (owned) bar;
> > >
> > > I don't have a strong opinion on this since I don't really need it, but
> > > using a cast expression feels a bit wrong. Not sure if we want to keep
> > > the option open of having operator overloading, but what about something
> > > like:
> > >
> > > string foo <= bar;
> > > or
> > > string foo << bar;
> >
> > In my opinion, this is not a lot clearer than the # syntax. The idea is
> > to use a more descriptive syntax so that reading code gets easier. As it
> > shouldn't be used often, a few characters more to type should not be an
> > issue.
>
> Yes, a descriptive syntax is very nice. However, I heard some good
> arguments to include the flow of data whenever possible. Anyway, in my
> opinion we probably shouldn't promote the explicit ownership transfer as
> a feature but rather as a necessity to get some things done. So, an odd
> syntax doesn't matter that much in this case.

Thanks. I get the point from you and jurg's argument.

Yu
> > Furthermore, please note that it needs to be an expression, it can also
> > be used as a method argument, not just in assignments.
> >
> > some_method (42, (owned) bar); 
> >
> > > >       * `unowned' type modifier complements `weak' type modifier
> > > >
> > > > `weak' only make sense for reference fields, list elements, and local
> > > > variables to break reference cycles. Vala will use
> > > > `g_object_add_weak_pointer' in these places in future versions.
> > >
> > > I definitely agree we should avoid dangling pointers as much as
> > > possible. However, I fear a bit that many people will turn to using
> > > pointers when this is also applied to local variables.
> >
> > Why do you think people will switch to pointers? Do you have an example
> > in mind where the change might cause issues?
>
> I don't see an immediate use case where this might fail. However, weak
> local variables can be used to tweak unnecessary reference counting
> overhead. Registering the pointers possibly invalidates this tweak. We
> have to wait an see how this actually behaves in for example loops etc.
> Judging from the implementation within GObject, weak references might
> actually be slower as strong ones.
> As a side note, we probably need to invent a similar functionality for
> non-GObject classes *if* we want to avoid dangling pointers all
> together. Also, I'm not sure how to treat the low level vala pointers in
> this case.
> Perhaps we can combine this with a compile option that is set by default
> to enable runtime checks.
>
> Hans
>
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