18. Minimum function with any number of arguments

It is possible to write function templates that can take a variable number of arguments using variadic function templates. For this, we need to implement compile-time recursion (which is actually just calls through a set of overloaded functions). The following snippet shows how the requested function could be implemented:

template <typename T>
T minimum(T const a, T const b) { return a < b ? a : b; }

template <typename T1, typename... T>
T1 minimum(T1 a, T... args)
{
   return minimum(a, minimum(args...));
}

int main()
{
   auto x = minimum(5, 4, 2, 3);
}

In order to be able to use a user-provided binary comparison function, we need to write another function template. The comparison function must be the first argument because it cannot follow the function parameter pack. On the other hand, this cannot be an overload of the previous minimum function, but a function with a different name. The reason is that the compiler would not be able to differentiate between the template parameter lists <typename T1, typename... T> and <class Compare, typename T1, typename... T>. The changes are minimal and should be easy to follow in this snippet:

template <class Compare, typename T>
T minimumc(Compare comp, T const a, T const b) 
{ return comp(a, b) ? a : b; }

template <class Compare, typename T1, typename... T>
T1 minimumc(Compare comp, T1 a, T... args)
{
   return minimumc(comp, a, minimumc(comp, args...));
}

int main()
{
   auto y = minimumc(std::less<>(), 3, 2, 1, 0);
}