Re: [Vala] idiomatic way to pass an array for modification to a function

[Felipe Lavratti <felipelav gmail com>]

Hi,

Everything is a reference in Vala, so, there's no buffer copy in your
example.

The rationale is opposite: Everything is passed as reference, if you want
to pass as copy, you have to set the parameter `owned`

```
void change_values(owned int[] w,int loc) { w[loc+0]=1; w[loc+1]=2;
w[loc+2]=3; }
```

Also, since you created an array with `new int[]` you should have an
parameter with the same construction, so that you variable `w` inside
`change_values` will have properties such as `.length`.

On Sun, Dec 27, 2015 at 6:24 PM Dan Hitt <dan hitt gmail com> wrote:

> I've been struggling to write a function that can modify an array it
> receives as an argument.
>
> Now, as it happens, it looks like you can just write it like it were
> C, using pointers.
>
> So this code works and does what i expect:
>
>     void main( ) {
>             var t = new int[6];
>             change_values(t, 0);
>             change_values(t, 3);
>             for (var i=0; i<t.length; i++)
>                     stdout.printf("%d -> %d\n",i,t[i]);
>     }
>
>     void change_values(int *w,int loc) {
>             w[loc+0]=1;
>             w[loc+1]=2;
>             w[loc+2]=3;
>     }
>
> However, it doesn't use 'ref' and i would like to write something more
> idiomatic.
>
> The constraint is that i really do want to have reference-type semantics
> with
> no unnecessary copying because the actual application will involve a
> routine
> called many times on a long input array.
>
> Thanks in advance for any clues on how to make this more stylistic, or any
> good
> but detailed references.  (This subject seems to come up from time to
> time, but the
> answers are never quite detailed enough for me to comprehend.)
>
> dan
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