synchronized (instanceLock) {
            stopActions = stopActions.plus(stopAction);
        }
    }

    @Override
    protected Value<? extends T> calculateOwnValue(ValueConsumer consumer) {
        return Value.of(getInstance());
    }

    private T getInstance() {
        listener.beforeGet(this);
        synchronized (instanceLock) {

                if (match == t) {
                    action.execute(match);
                }
            });
        }

        @Override
        protected Value<S> calculateOwnValue(ValueConsumer consumer) {
            if (ambiguous) {
                throw new IllegalStateException("Found multiple elements");
            }
            return Value.ofNullable(match);
        }
    }