// allows null keys but not null values

static <A, B> B getOrCreate(Map<A, B> map, A key, Class<? extends B> c) ctex {
  B b = map.get(key);
  if (b == null)
    map.put(key, b = c.newInstance());
  ret b;
}

// f : func -> B
static <A, B> B getOrCreate(Map<A, B> map, A key, O f) ctex {
  B b = map.get(key);
  if (b == null)
    map.put(key, b = (B) callF(f));
  ret b;
}

static <A, B> B getOrCreate(IF0<B> f, Map<A, B> map, A key) {
  ret getOrCreate(map, key, f);
}

static <A, B> B getOrCreate(Map<A, B> map, A key, IF0<B> f) {
  B b = map.get(key);
  if (b == null)
    map.put(key, b = f!);
  ret b;
}

static <A, B> B nuLike getOrCreate(Class<? extends B> c, Map<A, B> map, A key) {
  ret getOrCreate(map, key, c);
}