!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 {}