Re: [Vala] Confusing closure behavior

[Al Thomas <astavale yahoo co uk>]

   > On Monday, 8 April 2019, 23:01:05 BST, Vivien Kraus <vivien planete-kraus eu> wrote:  
> I have come across this weird closure thing.  In other programming
> languages, I would expect the closure in t to have a copy of i, but it
> only has a reference.  Is it expected?

That's an interesting question!

If you want a copy then pass it as an argument. If you want to usea variable from the enclosing scope then 
use a closure, but bewareif it changes in the enclosing scope it will change in the closure.

That was my initial thought. Kind of made sense until I read you expected other programming languages to make 
a copy.
If you look at the C code generated, use --ccode with valac, youwill see a struct, _data, is created to hold 
the enclosed variables.It makes sense then that i, although a value type, is a reference.
Now there are some rough edges with how Vala handles value typesin 
generics:https://gitlab.gnome.org/GNOME/vala/issues/564https://gitlab.gnome.org/GNOME/vala/merge_requests/52
If you think there is also a problem with closures then head overto 
https://gitlab.gnome.org/GNOME/vala/issues and make your case.

Al


> public delegate void Thunk();

> public static void run (Thunk t) {
>      t ();
> }

> int main() {
>      int i = 0;
>      Thunk t = () => {
>          stdout.printf ("%d = 0, right?\n", i);
>      };
>      i = 1;
>      run (t);
>      return 0;
> }