C++20 Returning Non-type Variadic Template Tuple

Question

Currently using g++11.3.0, C++20.

I'm trying to compile the code below, where the function foo takes an arbitrary number of template arguments and returns a tuple that contains a value for each template argument. The code compiles and runs for me when I use the statements foo<int>() and foo<float>(), but runs into an error when I use the statement foo<int, float>():

error: no viable conversion from returned value of type 'tuple<typename __unwrap_ref_decay<float>::type, (no argument)>' to function return type 'tuple<int, float>'

However, if I change the return type from std::tuple<Args...> to auto, it compiles and runs for all three statements. Is return type deduction the only way to go or is there a way to avoid using the auto keyword?

template <typename ...Args>
std::tuple<Args...> foo()
{
    return std::make_tuple(([] ()
    {
        // Do some stuff....
        // Return value....

        return Args();
    }(), ...));
}

Answer 1

You use the syntax for folding expression using comma operator, instead you need:

template <typename ...Args>
std::tuple<Args...> foo()
{
    return std::make_tuple([] ()
    {
        // Do some stuff....
        // Return value....

        return Args();
    }()...);
}