static <A, B> B getOrCreate_f0(Map<A, B> map, A key, F0<B> create) {
  B b = map.get(key);
  if (b == null)
    mapPut(map, key, b = callF(create));
  ret b;
}

static <A, B> B getOrCreate_f0(Map<A, B> map, A key, IF0<B> create) {
  B b = map.get(key);
  if (b == null)
    mapPut(map, key, b = callF(create));
  ret b;
}

Began life as a copy of #1021431