void tryDoSome(Out<bool> out) {
  trySetVal(out, true);
}

final out = Out<bool>();

tryDoSome(out);

out.val; // true

void addRef(Ref<int> ref) {
  tryChangeVal(ref, (val) => val + 1);
}

final ref = Ref(1);

addRef(ref);
addRef(ref);

ref.val; // 3