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  1. #include <iostream>
  2. #include <functional>
  3. #include <array>
  4. #include <cassert>
  5. #include <cstdlib>
  6. using namespace std;
  7.  
  8. template<typename T>
  9. class lazy {
  10. 	using init_func_t = function<T()>;
  11. 	mutable T value;
  12. 	mutable init_func_t init;
  13. public:
  14. 	lazy(init_func_t func): init(func){
  15. 		assert(init);
  16. 	}
  17.  
  18. 	lazy(const T &v): value(v){}
  19.  
  20. 	lazy(const lazy &other){
  21. 		lazy(other.init.target());
  22. 	}
  23.  
  24.  
  25. 	operator T() const{
  26. 		if(init){
  27. 			value = init();
  28. 			init = init_func_t();
  29. 		}
  30. 		return value;
  31. 	}
  32.  
  33. 	lazy<T> &operator=(const lazy<T> &other){
  34. 		if(other.init){
  35. 			init = init_func_t(other.init.target());
  36. 		}
  37. 		else{
  38. 			init = init_func_t();
  39. 			value = other;
  40. 		}
  41. 		return *this;
  42. 	}
  43. };
  44.  
  45. struct car{
  46. 	static constexpr size_t str_buff_size = 64;
  47. 	lazy<char *> model { []{return new char[str_buff_size];} };
  48. };
  49.  
  50. int main(){
  51. 	array<car, 5> cars;
  52. 	for(auto &car: cars){
  53. 		fgets(car.model, car::str_buff_size, stdin);
  54. 		printf(car.model);
  55. 	}
  56. 	return 0;
  57. }
Success #stdin #stdout 0s 3464KB
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stdin
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mazda
toyota
opel
audi
bmw
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mazda
toyota
opel
audi
bmw
https://ideone.com/QUOxuJ
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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