Method emplace

src/fl/stl/unordered_map_small.h:334–337

    // Emplace
    template <typename... Args>
    fl::pair<iterator, bool> emplace(Args&&... args) FL_NOEXCEPT {
        value_type kv(fl::forward<Args>(args)...);
        return insert(fl::move(kv));
    }

    // Erase — clears occupied bit, iterator stable
    iterator erase(iterator pos) FL_NOEXCEPT {