Elegant jump table abstraction

jump_table.h

struct not_found
{
};

template <typename TKey, typename TValue, TKey...>
struct JumpTable;

template <typename TKey, typename TValue>
struct JumpTable<TKey, TValue>
{
    TValue& operator[]([[maybe_unused]] TKey needed)
    {
        throw not_found{};
    }
};

template <typename TKey, typename TValue, TKey key, TKey... rest>
struct JumpTable<TKey, TValue, key, rest...> : JumpTable<TKey, TValue, rest...>
{
    TValue value;
    using super = JumpTable<TKey, TValue, rest...>;

    TValue& operator[](TKey k)
    {
        return key == k ? value : super::operator[](k);
    }
};


int fn1(int x)
{
    return x + 1;
}
int fn2(int x)
{
    return x + 2;
}
int fn3(int x)
{
    return x + 3;
}

int main()
{
    JumpTable<DispatchId,
              FuncType,
              DispatchId::Id1,
              DispatchId::Id2,
              DispatchId::Id3> jt;

    jt[DispatchId::Id1] = fn1;
    jt[DispatchId::Id2] = fn2;
    jt[DispatchId::Id3] = fn3;
}