adl_printables.cpp

#include <iostream>
#include <vector>
#include <tuple>

namespace foo
{
    template <typename T>
    struct print final
    {
        const T& _x;
        constexpr print(const T& x) noexcept : _x{x} 
        {
        }    
    };

    template <typename T>
    auto& operator<<(std::ostream& os, const print<std::vector<T>>& v)
    {
        for(const auto& x : v._x) os << x << " ";
        return os;
    }

    template <typename... Ts>
    auto& operator<<(std::ostream& os, const print<std::tuple<Ts...>>& v)
    {
        (os << ... << print{std::get<Ts>(v._x)});
        return os;
    }
}

int main()
{
    std::vector<int> v{1,2,3,4,5};
    std::cout << foo::print{v} << std::endl;
    
    auto t{std::make_tuple(std::vector<int>{1,2,3,4,5})};
    std::cout << foo::print{v} << std::endl;
}