fork download
copy 
  1. #include <deque>
  2. #include <memory>
  3. #include <iostream>
  4.  
  5. template<class T> class manager {
  6. 	static void construct(T* p, const T& val) {
  7. 		new((void*)p) T(val); }
  8. 	template<class U, class... Args>
  9. 	  static void construct(U* p, Args&&... args) {
  10. 		new((void*)p) T(std::forward<Args>(args)...); }
  11. 	class allocator: public std::allocator<T> {
  12. 	public:
  13. 		void construct(T* p, const T& val) {
  14. 			manager::construct(p, val); }
  15. 		template<class U, class... Args>
  16. 		  void construct(U* p, Args&&... args) {
  17. 			  manager::construct(p, std::forward<Args>(args)...); }
  18. 	//needed for deque ...dunno why it is using rebind for T
  19. 		template<class U> struct rebind {
  20. 			typedef typename std::conditional<
  21. 			  std::is_same<T,U>::value, allocator,
  22. 			  std::allocator<U>>::type other; };
  23. 	};
  24. 	std::deque<T, allocator> storage; //deque preserves pointers
  25. public:
  26. 	template<class... Args>
  27. 	  T* create(Args&&... args) {
  28. 		storage.emplace_back(std::forward<Args>(args)...);
  29. 		return &storage.back();
  30. 	}
  31. };
  32.  
  33. class special {
  34. 	friend class manager<special>;
  35. 	int i;
  36. 	special(int i): i(i) {}
  37. public:
  38. 	int get() const { return i; }
  39. };
  40.  
  41. int main() {
  42. 	manager<special> m;
  43. 	special* p = m.create(123);
  44. 	std::cout << p->get() << std::endl;
  45. }
  46.  
Success #stdin #stdout 0s 3428KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
123
https://ideone.com/ow23Oi
Overcomming the problem with private constructor and emplace_back()
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!