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#include <memory>

template <typename T, typename Alloc = std::allocator<T>>allocator<T> >
class Container {
  T *UnderlyingStorage;
  size_t NumElements;
  
  void CopyElements(T *From, T *To, size_t Count);
  
public:
  void reserve(size_t Count) {
    if (Count > NumElements) {
      Alloc A;
      T *P = A.allocate(Count); // Throws on failure
      try {
        CopyElements(UnderlyingStorage, P, NumElements);
      } catch (...) {
        A.deallocate(P, Count);
        throw;
      }
      UnderlyingStorage = P;
    }
    NumElements = Count;
  }
  
  T &operator[](size_t Idx) { return UnderlyingStorage[Idx]; }
  const T &operator[](size_t Idx) const { return UnderlyingStorage[Idx]; }
};