Can't understand a piece of C++ code with perfect forwarding and ellipses

Question

I can't understand what does the following piece of C++ code does:

template<typename... Ts>
void print(Ts &&... ts)
{
    ns::logger{ (print(std::forward<Ts>(ts)), ns::s{})... };
}

I see that there's perfect forwarding with variadic arguments, but what is happening in the line below precisely?

My guess is that an object of type ns::logger is being uniform initialized with a series of values but I'm not sure which ones.. is that ... a folding expression?

Answer 1

ns::logger is being initialized with a list of expressions (print(std::forward<Ts>(ts)), ns::s{}), one for each element in ts.

Each expression, in turn, uses a comma operator. It calls print(std::forward<Ts>(ts)) and discards its result (if any). Then it constructs ns::s{}, and that object becomes the result of the comma operator.

The net result is roughly equivalent to this pseudocode:

print(std::forward<Ts_1>(ts_1));
print(std::forward<Ts_2>(ts_2));
...
print(std::forward<Ts_N>(ts_N));

ns::logger{ns::s{}, ns::s{}, ... /* repeated N times */};