snipet of union in C++03 for KMC Advent Calendar 2013

union3.cpp

template <typename T>
class BetterU {
  bool is_allocated;
  union {  // 余分な構造体が必要ない
    T i;
    T* p;
  };
  void Clean() {
    if (IsAllocated()) { delete p; }
  }
  void Assign(T src) {
    if (IsAllocated()) {
      p = new T(src);
    } else {
      i = src;
    }
  }
 public:
  BetterU(T src, bool alloc) : is_allocated(alloc) { Assign(src); }
  BetterU(const BetterU& src) : is_allocated(src.is_allocated) { Assign(src.GetValue()); }
  BetterU& operator=(const BetterU& rhs) {
    if (IsAllocated() && rhs.IsAllocated()) {
        *p = *rhs.p;
    } else {
      Clean();
      is_allocated = rhs.IsAllocated();
      Assign(rhs.GetValue());
    }
    return *this;
  }
  ~BetterU() { Clean(); }
  T GetValue() const {
    if (IsAllocated()) {
      return *p;
    } else {
      return i;
    }
  }
  bool IsAllocated() const { return is_allocated; }
};