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  1. //#define BUG_CASE
  2.  
  3. #include <iostream>
  4. #include <deque>
  5. #include <algorithm>
  6. #include <utility>
  7. #include <memory>
  8. using namespace std;
  9.  
  10. deque<bool> pool;
  11.  
  12. class ExpressionTemp;
  13. class Scalar
  14. {
  15.     bool *alive;
  16.  
  17.     friend class ExpressionTemp;
  18.  
  19.     Scalar(const Scalar&);
  20.     Scalar &operator=(const Scalar&);
  21.     Scalar &operator=(Scalar&&);
  22. public:
  23.     Scalar()
  24.     {
  25.         pool.push_back(true);
  26.         alive=&pool.back();
  27.     }
  28.     Scalar(Scalar &&rhs)
  29.         : alive(0)
  30.     {
  31.         swap(alive,rhs.alive);
  32.     }
  33.     ~Scalar()
  34.     {
  35.         if(alive)
  36.             (*alive)=false;
  37.     }
  38. };
  39. class ExpressionTemp
  40. {
  41. #ifndef BUG_CASE
  42.     unique_ptr<Scalar> resource; // can be in separate type
  43. #endif
  44.     bool *operand_alive;
  45. public:
  46.     ExpressionTemp(const Scalar &s)
  47.         : operand_alive(s.alive)
  48.     {
  49.     }
  50. #ifndef BUG_CASE
  51.     ExpressionTemp(Scalar &&s)
  52.         : resource(new Scalar(move(s))), operand_alive(resource->alive)
  53.     {
  54.     }
  55. #endif
  56.     void do_job()
  57.     {
  58.       if(*operand_alive)
  59.           cout << "captured operand is alive" << endl;
  60.       else
  61.           cout << "captured operand is DEAD!" << endl;
  62.     }
  63. };
  64.  
  65. template<typename T>
  66. ExpressionTemp expression(T &&s)
  67. {
  68.     return {forward<T>(s)};
  69. }
  70. int main()
  71. {
  72.     {
  73.         expression(Scalar()).do_job(); // OK, Scalar is moved to temporary
  74.     }
  75.     {
  76.         Scalar lv;
  77.         auto &&rvref=expression(lv);
  78.         rvref.do_job(); // OK, lv is still alive
  79.     }
  80.     {
  81.         auto &&rvref=expression(Scalar());
  82.         rvref.do_job(); // OK, Scalar is moved into rvref
  83.     }
  84.     return 0;
  85. }
  86.  
Success #stdin #stdout 0s 3020KB
comments (?)
stdin 
Standard input is empty
stdout 
captured operand is alive
captured operand is alive
captured operand is alive
https://ideone.com/GYHhRZ
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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