Check if one set of types is a subset of the other

Question

How can one check if one parameter pack (interpreted as a set) is a subset of another one?

So far I only have the frame (using std::tuple), but no functionality.

Answer 1

If you can use C++17 features, I highly recommend using Piotr Skotnicki's solution!

I had to implement this functionality a while ago. I am just going to copy-paste the code I came up with at that point.

I am not claiming that this is the best or most elegant way to implement this kind of check! I did not bother thinking about the edge cases too much; you may need to adapt the code to fit your requirements.

To clarify: ContainsTypes checks if Rhs is a subset of Lhs.

---

  template 
  struct ContainsType;

  template 
  struct ContainsType, U>
  {
      static const bool VALUE = ContainsType, U>::VALUE;
  };

  template 
  struct ContainsType, T>
  {
      static const bool VALUE = true;
  };

  template 
  struct ContainsType, T>
  {
      static const bool VALUE = false;
  };

  // -----

  template 
  struct ContainsTypes;

  template 
  struct ContainsTypes>
  {
      static const bool VALUE = ContainsType::VALUE && ContainsTypes>::VALUE;
  };

  template 
  struct ContainsTypes>
  {
      static const bool VALUE = true;
  };