Method map

cpp/fory/meta/field_info.h:245–245

    return with_spec(spec_.set(elem));
  }
  constexpr FieldMeta map() const { return with_spec(spec_.map()); }
  constexpr FieldMeta map(FieldNodeSpec key, FieldNodeSpec value) const {
    return with_spec(spec_.map(key, value));
  }