id.h

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#ifndef __utl_container_id_h__
#define __utl_container_id_h__

#include <utl/core/impl.h>
#include <utl/container/array.h>
#include <algorithm>

namespace utl {

   template <typename _Tp, size_t _Nm>
   struct id_traits {
      typedef _Tp type[_Nm];

      static constexpr _Tp& Ref (const type& t, size_t n) noexcept {
         return const_cast<_Tp&> (t[n]);
      }

      static constexpr _Tp* Ptr(const type& t) noexcept {
         return const_cast<_Tp*> (t);
      }
   };

   template <typename _Tp>
   struct id_traits<_Tp, 0> {
      struct type { };

      static constexpr _Tp& Ref(const type& t, size_t n) noexcept {
         return *static_cast<_Tp*>(nullptr);
      }

      static constexpr _Tp* Ptr(const type& t) noexcept {
         return nullptr;
      }
   };

   template <typename _Tp, size_t _Nm>
   struct id_t {
      using value_type        = _Tp;
      using pointer           = value_type*;
      using const_pointer     = const value_type*;
      using reference         = value_type&;
      using const_reference   = const value_type&;
      using iterator          = value_type*;
      using const_iterator    = const value_type*;
      using size_type         = size_t;
      using difference_type   = std::ptrdiff_t;
      using reverse_iterator  = std::reverse_iterator <iterator>;
      using const_reverse_iterator
                              = std::reverse_iterator <const_iterator>;

      // type and data
      using traits_t              = id_traits<_Tp, _Nm>;
      typename traits_t::type    _data;

      // No explicit construct/copy/destroy for aggregate type.

      // DR 776 (std::array)
      void fill (const value_type& v) { std::fill_n (begin(), size(), v); }

      void swap (id_t& other) noexcept {
         std::swap_ranges (begin(), end(), other.begin());
      }

            iterator begin()        noexcept { return iterator (data()); }
      const_iterator begin()  const noexcept { return const_iterator (data()); }
            iterator end()          noexcept { return iterator (data() + _Nm); }
      const_iterator end()    const noexcept { return const_iterator (data() + _Nm); }
      const_iterator cbegin() const noexcept { return const_iterator (data()); }
      const_iterator cend()   const noexcept { return const_iterator (data() + _Nm); }

            reverse_iterator rbegin()        noexcept { return reverse_iterator (end()); }
            reverse_iterator rend()          noexcept { return reverse_iterator (begin()); }
      const_reverse_iterator rbegin()  const noexcept { return const_reverse_iterator (end()); }
      const_reverse_iterator rend()    const noexcept { return const_reverse_iterator (begin()); }
      const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator (end()); }
      const_reverse_iterator crend()   const noexcept { return const_reverse_iterator (begin()); }
      constexpr size_type size()     const noexcept { return _Nm; }
      constexpr size_type max_size() const noexcept { return _Nm; }
      constexpr      bool empty()    const noexcept { return size() == 0; }


      reference operator[] (size_type n) noexcept {
         return traits_t::Ref (_data, n);
      }
      constexpr const_reference  operator[] (size_type n) const noexcept {
         return traits_t::Ref (_data, n);
      }

      reference at (size_type n) noexcept {
         if (n < _Nm)
            return traits_t::Ref (_data, n);
         else
            abort ();
      }
      constexpr const_reference at (size_type n) const noexcept {
         static_assert ((n < _Nm), "id_t::at: out of range");
         return traits_t::Ref (_data, n);
      }
      constexpr bool bit (uint8_t bit) const noexcept {
         return traits_t::Ref (_data, bit/(8*sizeof(_Tp))) &
                (static_cast<value_type>(0x01) << ((bit % (8*sizeof(_Tp)))-1));
      }

      void bit (uint8_t bit, bool v) noexcept {
         value_type one = 1;
         uint8_t den = 8*sizeof(_Tp)/sizeof(uint8_t);
         if (v)   traits_t::Ref (_data, bit/den) |=  one << ((bit % den)-1);
         else     traits_t::Ref (_data, bit/den) &= ~one << ((bit % den)-1);
      }
      // first item
      reference front () noexcept {
         return *begin ();
      }
      constexpr const_reference front () const noexcept {
         return traits_t::Ref (_data, 0);
      }

      // Last item
      reference back () noexcept {
         return _Nm ? *(end() - 1) : *end();
      }
      constexpr const_reference back () const noexcept {
         return _Nm ? traits_t::Ref (_data, _Nm - 1)
                    : traits_t::Ref (_data, 0);
      }

      // Pointer to data
            pointer data ()       noexcept { return traits_t::Ptr (_data); }
      const_pointer data () const noexcept { return traits_t::Ptr (_data); }
   };

   template <typename _Tp, size_t _Nm>
   inline bool operator== (const id_t<_Tp, _Nm>& lhs, const id_t<_Tp, _Nm>& rhs) {
      return std::equal (lhs.begin(), lhs.end(), rhs.begin());
   }

   template <typename _Tp, size_t _Nm>
   inline bool operator!= (const id_t<_Tp, _Nm>& lhs, const id_t<_Tp, _Nm>& rhs) {
      return !(lhs == rhs);
   }

   template <typename _Tp, size_t _Nm>
   inline bool operator< (const id_t<_Tp, _Nm>& lhs, const id_t<_Tp, _Nm>& rhs) {
      // MSB plays bigger role in comparison
      return std::lexicographical_compare(lhs.rbegin(), lhs.rend(), rhs.rbegin(), rhs.rend());
   }

   template <typename _Tp, size_t _Nm>
   inline bool operator> (const id_t<_Tp, _Nm>& lhs, const id_t<_Tp, _Nm>& rhs) {
      return rhs < lhs;
   }

   template <typename _Tp, size_t _Nm>
   inline bool operator<= (const id_t<_Tp, _Nm>& lhs, const id_t<_Tp, _Nm>& rhs) {
      return !(lhs > rhs);
   }

   template <typename _Tp, size_t _Nm>
   inline bool operator>= (const id_t<_Tp, _Nm>& lhs, const id_t<_Tp, _Nm>& rhs) {
      return !(lhs < rhs);
   }

} // namespace utl


#endif /* __utl_container_id_h__ */