static create(
   sourceReference: VersionedPathReference<Opaque>,
   pathReference: PathReference<string>
 ) {
   if (isConst(pathReference)) {
     let path = pathReference.value();
     return referenceFromPath(sourceReference, path);
   } else {
     return new GetHelperReference(sourceReference, pathReference);
   }
 }

  compute() {
    let { lastPath, innerReference, innerTag } = this;
    let path = this.pathReference.value();

    if (path !== lastPath) {
      innerReference = referenceFromPath(this.sourceReference, path);
      innerTag.inner.update(innerReference.tag);
      this.innerReference = innerReference;
      this.lastPath = path;
    }

    return innerReference.value();
  }

 [UPDATE](value: any) {
   set(this.sourceReference.value(), this.pathReference.value(), value);
 }