Passing a class instance to a thread via spawn()

[Joseph Rushton Wakeling]

On Thursday, 18 July 2013 at 23:54:22 UTC, Ali Çehreli wrote:
> On 07/18/2013 04:23 PM, Joseph Rushton Wakeling wrote:
>
> > Hello all,
> >
> > I have a data structure which is a final class.  Once
> created, the contents of
> > the class will not be mutated (only its const methods will be
> called).
> >
> > Is there any way to pass this to a thread via spawn() or via
> message-passing?
> > I've seen instructions to use shared() but if I try and
> declare the class this
> > way I get errors such as "non-shared method is not callable
> using a shared
> > object" and "non-shared const method is not callable using a
> shared object".
> >
> > The ideal would be to mark this object, once created, as
> immutable -- but trusty
> > methods like assumeUnique() don't work for classes!
> >
> > Can anyone advise?
> >
> > Thanks & best wishes,
> >
> >       -- Joe
> >
>
> The following seems to work but it may have more 'immutable' 
> keywords than you need. For example, the final class F need not 
> be 'immutable'. I think it is the objects of it that you want 
> 'immutable'. (?)
>
> Anyway, the following may be a start:
>
> import std.concurrency;
> import core.thread;
>
> interface I
> {
>     int foo();
> }
>
> class C : I
> {
>     int i;
>
>     this(int i) immutable {
>         this.i = i;
>     }
>
>     override int foo() {
>         return 1;
>     }
> }
>
> immutable final class F : C
> {
>     double d;
>
>     this(int i, double d) immutable {
>         super(i);
>         this.d = d;
>     }
>
>     /* 'override' keyword is required if the class is 
> non-immutable
>      * and not required otherwise. Bug? */
>     int foo() {
>         return 2;
>     }
>
>     int bar() const {
>         return 3;
>     }
> }
>
> void worker(immutable(F) f)
> {
>     f.bar();
> }
>
> void main()
> {
>     auto f = new immutable(F)(42, 1.5);
>
>     spawn(&worker, f);
>
>     thread_joinAll();
> }
>
> Ali

That's a very interesting idea. Thanks so much for sharing! :-)