@CanIgnoreReturnValue // TODO(b/27479612): consider removing this
  public <K1 extends K, V1 extends V> CacheBuilder<K1, V1> weigher(
      Weigher<? super K1, ? super V1> weigher) {
    checkState(this.weigher == null);
    if (strictParsing) {
      checkState(
          this.maximumSize == UNSET_INT,
          "weigher can not be combined with maximum size (%s provided)",
          this.maximumSize);
    }

func (sys *IAMSys) periodicRoutines(ctx context.Context, baseInterval time.Duration) {
	// Watch for IAM config changes for iamStorageWatcher.
	watcher, isWatcher := sys.store.IAMStorageAPI.(iamStorageWatcher)
	if isWatcher {
		go func() {
			ch := watcher.watch(ctx, iamConfigPrefix)
			for event := range ch {
				if err := sys.loadWatchedEvent(ctx, event); err != nil {
					// we simply log errors

				"application/vnd.shana.informed.interchange",
				"application/vnd.shana.informed.package",
				"application/vnd.simtech-mindmapper",
				"application/vnd.smaf",
				"application/vnd.smart.teacher",
				"application/vnd.software602.filler.form+xml",
				"application/vnd.software602.filler.form-xml-zip",
				"application/vnd.solent.sdkm+xml",
				"application/vnd.spotfire.dxp",
				"application/vnd.spotfire.sfs",

// layer.
type IAMStoreSys struct {
	IAMStorageAPI

	group  *singleflight.Group
	policy *singleflight.Group
}

// HasWatcher - returns if the storage system has a watcher.
func (store *IAMStoreSys) HasWatcher() bool {
	_, ok := store.IAMStorageAPI.(iamStorageWatcher)
	return ok
}

// GetUser - fetches credential from memory.