!7

// Makes the Concept.Ref object unnecessary by directly

// storing the reference in a field.

// We can probably get rid of the refs field in the same go.

// Of course, backRefs are still needed.

// TODO: We need backRefs to be able to store concepts also

// (by changing its type to L).

// Or we add another field directBackRefs.

sbool isConceptRefValid(Concept src, Concept dest) {

  ret src != null && dest != null && src._concepts != null && src._concepts == dest._concepts;

}

svoid indexConceptRef(Concept src, Concept dest) {

  if (isConceptRefValid(src, dest)) {

    // dest._addBackRef(src);

    change();

  }

}

svoid unindexConceptRef(Concept src, Concept dest) {}

sO conceptRefMutex(Concept c) {

  ret or(c._concepts, dummyMutex());

}

concept Thing {

  Thing ref_ptr;

  // setter

  selfType ref(Thing dest) {

    synchronized(conceptRefMutex(this)) {

      if (ref_ptr != dest) {

        unindexConceptRef(this, ref_ptr);

        ref_ptr = dest;

        indexConceptRef(this, dest);

      }

    }

    this;

  }

  // getter. we could get rid of this by making the field

  // publicly accessible, but then we run the slight chance

  // of setting it without the setter inadvertently.

  Thing ref() { ret ref_ptr; }

}

cprint {}