Re: [Vala] Vala : Suggestion for improvement : String Class wrapper for strings in Vala : Addendum

[Гаврилов Максим <ulltor gmail com>]

It's not a bug, but just two ways to write the same thing: in Vala-style or
in C-style.
21.06.2011 22:18 пользователь "Serge Hulne" <serge hulne gmail com> написал:
> Apparently
>
> string a = "hello";
> string * b = a;
>
> and :
>
> string a = "hello";
> unowned string b = a;
>
> appear to be translated by Vala into the exact same C code.
>
> Are these two ways to declare the same thing or is this just a bug which
> happens to work perchance ?
>
> Serge.
>
>
>
> On Tue, Jun 21, 2011 at 8:02 PM, Serge Hulne <serge hulne gmail com>
wrote:
> > Erratum:
> > =======
> >
> > As Alexandre Rosenfeld correctly pointed out, the easy (and correct)
> > way to get a reference on a Vala string is simply to declare it as
> > follows:
> >
> > string a = "hello";
> > string * b = a;
> >
> > As illustrated in the following snippet:
> >
> > ///
> > void main (string[] argv) {
> >
> > string a = "hello";
> > string * b = a;
> >
> > stdout.printf("Value of a = %s\n", a);
> > stdout.printf("Value of b = %s\n", b);
> > }
> > ///
> >
> > Which yields :
> >
> > Value of a = hello
> > Value of b = hello
> >
> > the corresponding C code generated by Vala being:
> >
> >
> > ///----------------
> > /* test_ref.c generated by valac 0.12.1, the Vala compiler
> > * generated from test_ref.vala, do not modify */
> >
> >
> > #include <glib.h>
> > #include <glib-object.h>
> > #include <stdlib.h>
> > #include <string.h>
> > #include <stdio.h>
> >
> > #define _g_free0(var) (var = (g_free (var), NULL))
> >
> >
> >
> > void _vala_main (gchar** argv, int argv_length1);
> >
> >
> > void _vala_main (gchar** argv, int argv_length1) {
> > gchar* _tmp0_;
> > gchar* a;
> > const gchar* b;
> > _tmp0_ = g_strdup ("hello");
> > a = _tmp0_;
> > b = a;
> > fprintf (stdout, "Value of a = %s\n", a);
> > fprintf (stdout, "Value of b = %s\n", b);
> > _g_free0 (a);
> > }
> >
> >
> > int main (int argc, char ** argv) {
> > g_type_init ();
> > _vala_main (argv, argc);
> > return 0;
> > }
> > ///---------
> >
> > In which there is indeed no duplication of memory allocation.
> >
> > as can be seen from:
> > _tmp0_ = g_strdup ("hello");
> > a = _tmp0_;
> > b = a;
> >
> >
> > Serge.
> >
> >
> > On Tue, Jun 21, 2011 at 9:05 AM, Serge Hulne <serge hulne gmail com>
> > wrote:
> > > Suggestion:
> > > =========
> > > A class wrapper for the string type in Vala, in order to avoid
> > > duplication of data in assignments (which would yield an unnecessarily
> > > huge memory usage when processing a large amount of text with a lot of
> > > assignments).
> > >
> > > if you compare the C code generated by Vala for:
> > >
> > > 1)
> > >
> > > ///
> > > class String {
> > > public string s;
> > > }
> > >
> > > void main (string[] argv) {
> > > String a = new String();
> > > a.s = "hello";
> > > String b = a;
> > > stdout.printf("a.s = %s\n", a.s);
> > > stdout.printf("b.s = %s\n", b.s);
> > > }
> > > ///
> > >
> > >
> > > To :
> > >
> > > 2) the C code generated by Vala for:
> > >
> > > ///
> > > void main (string[] argv) {
> > > string a = "hello";
> > > string b = a;
> > > stdout.printf("a = %p\n", &a);
> > > stdout.printf("b = %p\n", &b);
> > > }
> > > ///
> > >
> > > You will notice that in the second case (the naive straightforward
> > > formulation) the data is duplicated (passed by value in the
> > > assignment) whereas in the first case (which uses a class wrapper) the
> > > object a is assigned to b by reference (not by value, i.e. the data is
> > > not duplicated)
> > >
> > >
> > > Serge.