Question

How would you write a template function that takes a variable number of homogeneous non-POD function arguments in C++11?

For example suppose we wanted to write a min function for any type that defines the less than “operator<” as follows:

// pseduo-code...

template<class T...>
T min(T x1, T x2, ..., T xn)
{
    T lowest = x1;

    for (T x : {x2,...,xn})
       if (x < lowest)
           lowest = x;

    return lowest;
}

The above is illegal C++11, how would you write it legally?

Answer 1

Homogeneous? Just use std::initializer_list.

template <typename T>
T min_impl(std::initializer_list<T> values)
{
    return *std::min_element(values.begin(), values.end());
}

...

return min_impl({8, 5, 4, 1, 6});

(As @Jesse noted, this is the equivalent to std::min in the standard library.)

If you don’t like the extra braces, make a variadic template that forwards to the initializer list implementation:

template <typename... T>
auto min(T&&... args) -> decltype(min_impl({std::forward<T>(args)...}))
{
    return min_impl({std::forward<T>(args)...});
}

...

return min(8, 5, 1, 4, 6);