static AutoCloseable tempSetField(O o, S field, O value) {
  fO oldValue = get(o, field);
  set(o, field, value);
  ret () -> set(o, field, oldValue);
}

static <A> AutoCloseable tempSetField(ISetAndGet<A> gs, A value) {
  if (gs == null) null; // convenient null propagation as always in JavaX!
  A oldValue = gs!;
  gs.set(value);
  ret () -> gs.set(oldValue);
}

static <A> AutoCloseable tempSetField(A value, ISetAndGet<A> gs) {
  ret tempSetField(gs, value);
}