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

[Serge Hulne <serge hulne gmail com>]

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.