How can I pretty-print a std::tuple using variadic templates in C ?

Pretty Printing std::tuple

In a previous question, we discussed a general solution for pretty-printing STL containers. Now, let's extend that solution to handle std::tuple using variadic templates (C 11 or later).

Analogous Construction for Printing a Tuple

Similar to std::pair, pretty-printing a tuple involves enclosing the elements within parentheses and separating them with commas. The goal is to achieve the following behavior:

auto a = std::make_tuple(5, "Hello", -0.1);
std::cout << a << std::endl; // prints: (5, "Hello", -0.1)

Variadic Solution

To accomplish this, we utilize variadic templates along with a helper struct for generating a sequence of indices. Here's the solution:

namespace aux {
    template<std::size_t... Is> struct seq{};

    template<std::size_t N, std::size_t... Is>
    struct gen_seq : gen_seq<N-1, N-1, Is...>{};

    template<std::size_t... Is>
    struct gen_seq<0, Is...> : seq<Is...>{};

    template<class Ch, class Tr, class Tuple, std::size_t... Is>
    void print_tuple(std::basic_ostream<Ch, Tr>& os, Tuple const& t, seq<Is...>) {
        using swallow = int[];
        (void)swallow{0, (void(os << (Is == 0? "" : ", ") << std::get<Is>(t)), 0)...};
    }
} // aux::

template<class Ch, class Tr, class... Args>
auto operator<<(std::basic_ostream<Ch, Tr>& os, std::tuple<Args...> const& t)
    -> std::basic_ostream<Ch, Tr>& {
    os << "(";
    aux::print_tuple(os, t, aux::gen_seq<sizeof...(Args)>());
    return os << ")";
}

This solution elegantly prints tuples using comma-separated elements enclosed in parentheses.

Custom Delimiters

For added flexibility, you can include custom delimiters for tuples by adding the following partial specializations:

// Delimiters for tuple
template<class... Args>
struct delimiters<std::tuple<Args...>, char> {
    static const delimiters_values<char> values;
};

template<class... Args>
const delimiters_values<char> delimiters<std::tuple<Args...>, char>::values = { "(", ", ", ")" };

template<class... Args>
struct delimiters<std::tuple<Args...>, wchar_t> {
    static const delimiters_values<wchar_t> values;
};

template<class... Args>
const delimiters_values<wchar_t> delimiters<std::tuple<Args...>, wchar_t>::values = { L"(", L", ", L")" };

By incorporating these specializations, you can customize the delimiters for std::tuple as well.

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