Re: [Vala] Read object's properties

[Philipp Trommler <keinerschreibtmirwas msn com>]

Hi!

Am Dienstag, den 24.03.2015, 09:43 +0100 schrieb Richard Wiedenhöft:
> Hi,
>
> The sizeof-function is actually a constant expression that is
> evaluated during compile-time. So in your binary there is no actual
> call to it.

Good to hear that.

> Sizeof works fine for every data-type in C. When your data type is or
> contains
> pointers just copying the memory-chunk will not do the job because the
> references
> do not mean anything in a different context.

That is just what I thought why it wasn't working. I just hoped there
was an easy way to go around that (some kind of: Vala creates all that
structs during compilation so there has to be a way Vala can collect
them again to measure their size and get their addresses).

> If you want to save certain objects to disk i'd suggest you write an
> Interface containing a serialize and unserialize function. This way
> you also avoid saving
> temporary state that can be reconstructed using other data.

I'll try this.

Thanks,
Philipp.

> Greetings,
> Richard
>
> Am 24.03.2015 um 08:11 schrieb Philipp Trommler:
>
> > Hi!
> >
> > Thanks for the advice, it works.
> > But isn't there a more general way to achieve my goal? A way to access
> > all the data from an instance? And why does the `sizeof` function
> > doesn't work correctly for classes?
> > I looked into the generated C sources and understand that a Vala class
> > is split into several structs but my knowledge of C (and the GObject
> > system in special) isn't that good, so I cannot implement a save
> > function in C myself (at least not yet and I would still prefer to do it
> > in Vala).
> > But from a user's point of view I have to say that I expected the normal
> > `sizeof` to work with all data types and still think so. Where is the
> > sense of a `sizeof` function for data types which size is already known?
> > Why should I test everytime at runtime for the size of e.g. an int?
> > Don't get me wrong, I still like Vala ;-) But I'm a little bit shocked
> > that there seems to be no way to simply read a class directly from
> > memory.
> >
> > Hope somebody proofs me wrong,
> > Philipp.
> >
> >
> > Am Montag, den 23.03.2015, 13:10 +0100 schrieb Andrea Del Signore:
> > > Hi,
> > >
> > >
> > > because you defined the "attributes" as fields (eg. private class
> > > instance variable) and not a properties.
> > >
> > >
> > > See https://wiki.gnome.org/Projects/Vala/Tutorial#Properties for more
> > > details.
> > >
> > >
> > > Try to change the Test class as:
> > >
> > > public class Test : GLib.Object, Saveable {
> > >         public string name { get; private set; }
> > >         public int zahl { get; private set; }
> > >
> > >         private List<string> liste;
> > >
> > >         public bool boolean { get; set; }
> > >         protected uint16 kleine;
> > >
> > >         internal int32 integ;
> > >
> > >         public Test (string name, int zahl, List<string> liste) {
> > >                 this.name = name;
> > >                 this.zahl = zahl;
> > >                 this.liste = liste.copy ();
> > >         }
> > > }
> > >
> > >
> > > you should at least see the name, zahl and boolean properties listed
> > > when calling the save_object function.
> > >
> > >
> > > Ciao,
> > >
> > > Andrea
> > >
> > >
> > >
> > >
> > >
> > > On Mon, Mar 23, 2015 at 12:15 PM, Philipp Trommler
> > > <keinerschreibtmirwas msn com> wrote:
> > >         Hi!
> > >         
> > >         This is my first post on this list so I just want to say hello
> > >         to
> > >         everybody. My name is Philipp Trommler, I'm from Dresden,
> > >         Germany and
> > >         I'm programming Vala as a hobby. I really like Vala as I like
> > >         the
> > >         syntax, the fact that it's performant and the good integration
> > >         into the
> > >         gnome ecosystem. In the last days I wanted to dig a bit deeper
> > >         into
> > >         serious Vala programming what leads me to my question:
> > >         
> > >         What are common ways to access an object's attributes? I
> > >         checked and
> > >         tried `GLib.ParamSpec` but receiving an empty array all the
> > >         time. Is
> > >         there any other method?
> > >         
> > >         The background is that I want to save an object's attributes
> > >         into a
> > >         file. Alternatively I would save the whole object (that's what
> > >         I tried
> > >         before, without luck, because I can't figure out how to access
> > >         all of
> > >         the object's parts in memory), but accessing the attributes
> > >         would be
> > >         enough for now.
> > >         
> > >         Maybe I'm just doing something wrong, so here's my code:
> > >         
> > >         ```
> > >         public interface Saveable : GLib.Object {
> > >                 public virtual void save_object (string filename) {
> > >                         unowned GLib.ObjectClass object_class =
> > >         this.get_class ();
> > >                         GLib.File file = GLib.File.new_for_path
> > >         (filename);
> > >                         GLib.FileOutputStream file_output_stream =
> > >         file.create
> > >         (GLib.FileCreateFlags.PRIVATE |
> > >         GLib.FileCreateFlags.REPLACE_DESTINATION);
> > >                         foreach (GLib.ParamSpec param_spec in
> > >         object_class.list_properties ())
> > >         {
> > >                                 stdout.printf ("%s\n",
> > >         param_spec.get_name ());
> > >                         }
> > >                 }
> > >         }
> > >         
> > >         public class Test : GLib.Object, Saveable {
> > >                 private string name;
> > >                 private int zahl;
> > >                 private List<string> liste;
> > >         
> > >                 public bool boolean;
> > >                 protected uint16 kleine;
> > >         
> > >                 internal int32 integ;
> > >         
> > >                 public Test (string name, int zahl, List<string>
> > >         liste) {
> > >                         this.name = name;
> > >                         this.zahl = zahl;
> > >                         this.liste = liste.copy ();
> > >                 }
> > >         }
> > >         ```
> > >         
> > >         So, as you can see, the class `Test` has some attributes. Why
> > >         can't I
> > >         access any of them?
> > >         
> > >         Greetings,
> > >         Philipp.
> > >         
> > >         _______________________________________________
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> > >         
> >
> >
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