generic_tostring_example.cpp

#include <iostream>
#include <string>
#include <type_traits>

template <typename T>
std::enable_if_t<std::is_convertible_v<T, std::string>, std::string>
    toString(const T& value)
{
    return { value };
}

namespace details
{
    template <typename T>
    constexpr auto canCallStdString = !std::is_same_v<T, bool> &&
                                      (std::is_integral_v<T> ||
                                       std::is_unsigned_v<T> ||
                                       std::is_floating_point_v<T>);
}

template <typename T>
std::enable_if_t<details::canCallStdString<T>, std::string>
    toString(const T& value)
{
    return std::to_string(value);
}

std::string toString(bool b)
{
    return b ? "true" : "false";
}

namespace details
{
    template <typename Type>
    struct HasToString {
    private:
        template<typename T>
        static constexpr auto check(T*) -> typename std::is_same<
                                                                 decltype(std::declval<T>().toString()), 
                                                                 std::string
                                                                 >::type;

        template<typename>
        static constexpr std::false_type check(...);

        using type = decltype(check<Type>(nullptr));

    public:
        static constexpr bool value = type::value;
    };
}

template <typename T>
constexpr auto HasToString = details::HasToString<T>::value;

template <typename T>
std::enable_if_t<HasToString<T>, std::string>
    toString(const T& value)
{
    return value.toString();
}


struct Pos
{
    int x, y;
    
    std::string toString() const
    {
        return "x: " + std::to_string(x) + ", y: " + std::to_string(y);
    }  
};


template <typename ...Args>
void print(const Args&... args)
{
    ( std::cout<< ... << (toString(args) + "\n") );
}

int main()
{
    int foo{ -20 };
    double bar{ 13.22 };
    bool baz{ false };
    std::string qux{ "qux" };
    Pos alohomora{ 20, 40 };
    
    print(foo, bar, baz, qux, "Pos: ", alohomora);
    
    return 0;
}