Set.hpp (cpp-lecture/nim2/Set.hpp)

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/*
   IsMemberInSet is a template helper class that allows
   to determine at compile-time if a non-negative integers
   is included in a set of non-negative integers.

   The first parameter of the template is the integer
   to be tested for membership, all other parameters
   specify the actual set.

   Examples:

      * IsMemberInSet<2, 0, 1, 2, 3>::is_member is true
        as 2 is included in {0, 1, 2, 3}

      * IsMemberInSet<2>::is_member is false
        as 2 is not member of {}
*/

#ifndef SET_HPP
#define SET_HPP

template<unsigned int candidate, unsigned int ... members>
struct IsMemberInSet;

/* partial template specialization for the empty set which
   ends the recursion */
template<unsigned int candidate>
struct IsMemberInSet<candidate> {
   public:
      static constexpr bool is_member = false;
};

/* partial template specialization for the recursive case where
   we compare the candidate with the first member of the set and then
   recursively with the rest of the set */
template<unsigned int candidate, unsigned int first_member,
   unsigned int ... other_members>
struct IsMemberInSet<candidate, first_member, other_members...> {
   public:
      static constexpr bool is_member = (candidate == first_member) ||
              IsMembercandidatecandiother_membersembers...>::is_member;
};

#endif