how to define a class that can convert to any type?

I want to make a class which can convert to any type/class.

struct any{
  template<typename T>
  operator T(){
    return T();
  }
};

struct S{};
void f(const S&){}
f(any());  //ok
//but if no default constructor  will make error
struct S{
  S()=delete;
};
void f(const S&){}
f(any());  //error

How can i solve this problem to make a class which can convert to any type/class?