absl::btree_map::try_emplace

template<
    class K = key_type,
    int = (EnableIf<LifetimeBoundK<K, false, IfRRef<const int &>::AddPtr<K>>>()),
    class... Args>
decltype(auto)
try_emplace(
    const_iterator hint,
    key_arg<K> const& k,
    Args&&... args);