Re: [Vala] Debugging

[Brian Duffy <brduffy gmail com>]

Okay, that was enlightening. I certainly am glad that I have some way to
investigate the clutter property but I can't help but wonder how hard it
would be for gdb to be able to print that value if I can print it right
from my vala code to the external console with a simple printf statement. I
guess it gets back to the fact that gdb is for debugging C and has no
knowledge of the hoops Vala is jumping through to get its printf function
to print out the value of that property. I see that as a problem, but not
as big a problem as writing my app in C versus Vala ;-)

On Sat, Dec 17, 2011 at 11:18 AM, Andrea Bolognani <eof kiyuko org> wrote:

> On Sat, Dec 17, 2011 at 10:42:00AM -0500, Brian Duffy wrote:
>
> > My compiler arguments have always been -g --pkg clutter-1.0 --save-temps
> ...
> > Actually, I just set a break point in my code and tried to inspect the
> > property value of a clutter object that had been instantiated. It seems
> > that gdb can't read the value of this property at the vala code page
> level.
> > It can however read the values of variables that I have defined in vala
> > itself (such as a loop counter variables). Someone on stackoverflow
> > recommended I use clutter_actor_get_width(r) where "r" is the name of the
> > clutter Rectangle that had been instantiated. I typed that into the
> > immediate window in monodevelop (using gdb debugger) and that returned my
> > value. I still have not gotten an answer I can understand as to why I
> can't
> > read property values of clutter objects when I break in my vala code
> > without calling a clutter function. I can print the value out with printf
> > and look at it in the external console but I can't evaluate the value
> with
> > the debugger. Strange, but thanks for the feedback.
>
> That’s due to the way Vala and GObject work.
>
> In C with GObject (which is the default target language of valac) instances
> are usually represented as opaque stuctures (see eg. [1] for
> ClutterRectangle), so if you have a rectangle the following C instruction
>
>        g_print ("%d\n", rectangle->border_width);
>
> won’t work as expected. Instead, you have to use an accessor method to
> retrieve the value assigned to an object property, as in
>
>        g_print ("%d\n", clutter_rectangle_get_border_width (rectangle));
>
> which will do what you want. You don’t need to do the same for your loop
> counters because those are “simple” types, so no accessors are involved.
>
> Does it seems verbose? It certainly is. Avoiding that verbosity, while
> still
> getting pretty much the same performance, is one of the main reasons to use
> Vala instead of plain C with GObject.
>
>
> [1] http://docs.clutter-project.org/docs/clutter/1.8/ClutterRectangle.html
> --
> Andrea Bolognani <eof kiyuko org>
> Resistance is futile, you will be garbage collected.
>
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-- 
Duff