Overload tuple indexing operator - C++

Question

How can I overload indexing [] operator for std::tuple<int,int,int>? So when I have std::tuple<int,int,int> tup and I type tup[0] I want it to return the reference to get<0>(tup). Is this possible?

Answer 1

As mentioned in other answers - it is not possible to add any member function to std type like std::tuple. And operator[] has to be non-static member function.

But you can wrap this tuple - and add operator[] to this wrapper type. In such case - you would need to know the common return type for all elements of tuple. Well - there is std::any which can work for most of types.

This should work, but this is only to meet your curiosity - it would be bad design to use something like that in real software:

template <typename Tuple, typename ReturnType = std::any>
class TupleExtractor
{
public:
    TupleExtractor(const Tuple& tuple) 
        : TupleExtractor(tuple, std::make_index_sequence<std::tuple_size_v<Tuple>>{})
    {}
    
    ReturnType operator[](std::size_t index) const
    {
        return extractors[index](tuple);
    }

private:
    template <std::size_t I>
    static ReturnType get(const Tuple& tuple)
    {
        return std::get<I>(tuple);
    }


    template <std::size_t ...I>
    TupleExtractor(const Tuple& tuple, std::index_sequence<I...>) 
        : tuple(tuple), 
          extractors{&TupleExtractor::get<I>...}
    {}

    const Tuple& tuple;
    using Extractor = ReturnType(*)(const Tuple&);
    std::vector<Extractor> extractors;
};

and test - that it works:

int main() {
    std::tuple<int, int, int> a{1,2,3};
    TupleExtractor e{a};
    
    return std::any_cast<int>(e[2]);
}