How to use user-defined deduction guides for multiple template parameters?

Question

Can I use user-defined deduction guides for classes with multiple template parameter? I want that one specified template parameter gets deduced from the constructor argument. All other template parameters must be specified in the <>-bracket when constructing a class. Example:

#include <iostream>

template<typename T, typename A>
struct Hello
{
    Hello(T x) : x(x) {}
    T x;
    A y;
};

Hello<A>(int) -> Hello<int, A>; // This is not a valid syntax but shows what i want to do 

int main()
{    
    Hello h = Hello<float>((int)1); // this should be deduced to Hello<int, float>
    std::cout << h.x << std::endl;
    return 0;
}

Answer 1

I could think about three approaches.

template <typename T, typename A>
struct Hello {
  Hello(T x) : x(x) {}
  T x;
  A y;
};

// Approach 1: use type aliases
// Requires at least c++-11

template <typename A>
using HelloInt = Hello<int, A>;

// Approach 2: use function factories

template <typename A>
Hello<int, A> make_hello_int(int i) {
    return Hello<int, A>(i);
}

// Approach 3: use template partial deduction

template <typename A, typename T>
Hello<T, A> make_hello(T i) {
  return Hello<T, A>(i);
}

int main() {
  // `auto` requires at least c++-11
  auto k = HelloInt<float>(1);
  std::cout << k.x << std::endl;
  std::cout << make_hello_int<float>(2).x << std::endl;
  std::cout << make_hello<float>(3).x << std::endl;
  return 0;
}