Passing a class instance to a thread via spawn()

[Ali Çehreli]

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