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  1. #include <iostream>
  2. #include <memory>
  3.  
  4. using namespace std;
  5.  
  6.     template< typename T, typename TProlog, typename TEpilog ,
  7.               bool call_epilog_due_to_prolog_exeption=true>
  8.     class decorator
  9.     {
  10.         TProlog prolog;
  11.         struct TDeleter
  12.         {
  13.             std::shared_ptr<T> ptr;
  14.             TEpilog epilog;
  15.             void operator() (T*p)
  16.             {
  17.                 // assert( p == ptr.get() )
  18.                 epilog();
  19.             }
  20.         } deleter;
  21.  
  22.     public:
  23.         decorator(std::shared_ptr<T> ptr, TProlog prolog, TEpilog epilog)
  24.             : prolog(prolog), deleter({ptr, epilog })
  25.         {}
  26.         decorator(const decorator&) = default;
  27.         decorator(decorator&&) = default;
  28.  
  29.         std::shared_ptr<T> operator->() const
  30.         {
  31.             return get();
  32.         }
  33.  
  34.         std::shared_ptr<T> get() const
  35.         {
  36.             if(call_epilog_due_to_prolog_exeption)
  37.             {
  38.                 std::shared_ptr<T> result( deleter.ptr.get(), deleter );
  39.                 prolog();
  40.                 return result;
  41.             }
  42.             else
  43.             {
  44.                 prolog();
  45.                 std::shared_ptr<T> result( deleter.ptr.get(), deleter );
  46.                 return result;
  47.             }
  48.         }
  49.     };
  50.  
  51.     template< typename T, typename TProlog, typename TEpilog >
  52.     decorator<T,TProlog,TEpilog>
  53.     decorate_ptr(std::shared_ptr<T> ptr, TProlog prolog, TEpilog epilog)
  54.     {
  55.         return decorator<T,TProlog,TEpilog>(ptr, prolog, epilog);
  56.     }
  57.  
  58.     template< typename T, typename TProlog, typename TEpilog >
  59.     decorator<T,TProlog,TEpilog>
  60.     decorate_obj(T& obj, TProlog prolog, TEpilog epilog)
  61.     {
  62.         std::shared_ptr<T> ptr( &obj, [](void*){} ); // no call 'delete'
  63.         return decorator<T,TProlog,TEpilog>(ptr, prolog, epilog);
  64.     }
  65.  
  66.  
  67.  
  68.     class FooTest
  69.     {
  70.     public:
  71.         void foo()
  72.         {
  73.             std::cout << "foo()" << std::endl;
  74.         }
  75.     } foo_test;
  76.  
  77.  
  78.     int main()
  79.     {
  80.         auto foo_ptr = decorate_obj(foo_test,
  81.                                     [](){  std::cout<<"prolog()"<<std::endl;  } ,
  82.                                     [](){  std::cout<<"epilog()"<<std::endl;  } );
  83.         foo_ptr->foo();
  84.  
  85.         return 0;
  86.     }
  87.  
Success #stdin #stdout 0s 15240KB
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Standard input is empty
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prolog()
foo()
epilog()
https://ideone.com/fQC5wT
language:
C++14 (gcc 8.3)
created:
5 years ago
visibility:
public

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