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  1. // Remove "x" to invoke feature.
  2. #define     xTEST_ABSTRACT_CLONE
  3.  
  4. #if defined( CPP11 )
  5. #   define OVERRIDE     override
  6. #   define IS_DELETED   = delete
  7. #   include <memory>
  8.     template< class Type >
  9.     struct Ownership { using Ptr = std::unique_ptr<Type>; };
  10. #else
  11. #   define OVERRIDE
  12. #   define IS_DELETED
  13. #   include <memory>        // Note: std::auto_ptr is deprecated.
  14.     template< class Type >
  15.     struct Ownership { typedef std::auto_ptr<Type> Ptr; };
  16. #endif
  17.  
  18. //---------------------------------------------------------------------------
  19. #include <assert.h>         // assert
  20. #include <iostream>         // std::wcout, std::wcerr, std::endl
  21. #include <memory>           // std::unique_ptr
  22. #include <string>           // std::string
  23. #include <typeinfo>         // std::typeinfo, i.e. typeid usage.
  24. using namespace std;
  25.  
  26. class Person
  27. {
  28. private:
  29.     string  name_;
  30.  
  31.     Person& operator=( Person const& ) IS_DELETED;
  32.  
  33.     virtual Person* virtualClone() const
  34.     {
  35.         assert( typeid( *this ) == typeid( Person ) );
  36.         return new Person( *this );
  37.     }
  38.  
  39. public:
  40.     string name() const { return name_; }
  41.  
  42.     Ownership<Person>::Ptr clone() const
  43.     {
  44.         return Ownership<Person>::Ptr( virtualClone() );
  45.     }
  46.  
  47.     Person( string const& name )
  48.         : name_( name )
  49.     {}
  50. };
  51.  
  52. class Student
  53.     : public Person
  54. {
  55. private:
  56.     int     studentId_;
  57.  
  58.     Student& operator=( Student const& ) IS_DELETED;
  59.  
  60.     virtual Student* virtualClone() const OVERRIDE
  61.     {
  62.         assert( typeid( *this ) == typeid( Student ) );
  63.         return new Student( *this );
  64.     }
  65.  
  66. public:
  67.     int studentId() const { return studentId_; }
  68.  
  69.     Ownership<Person>::Ptr clone() const
  70.     {
  71.         return Ownership<Person>::Ptr( virtualClone() );
  72.     }
  73.  
  74.     Student( string const& name, int const studentId )
  75.         : Person( name ), studentId_( studentId )
  76.     {}
  77. };
  78.  
  79. wostream& operator<<( wostream& stream, string const& s )
  80. {
  81.     return (stream << s.c_str());
  82. }
  83.  
  84. int main()
  85. {
  86.     Person                  a( "Hillary Clinton" );
  87.     Student                 b1( "John Smith", 12345 );
  88.     Student                 b2( "Mary Jones", 88888 );
  89.     Person&                 bAsPerson = b1;      // OK.
  90.     Ownership<Person>::Ptr  pClone;
  91.  
  92.     wcout
  93.         << "Name: " << b1.name()
  94.         << ". Student id: " << b1.studentId() << "."
  95.         << endl;
  96.  
  97. #ifdef TEST_ABSTRACT_CLONE
  98.     pClone = bAsPerson.clone(); // OK, clones John Smith the Student.
  99. #else
  100.     pClone = b2.clone();        // More obviously (?) OK, clones Mary.
  101. #endif
  102.     Student& studentRef = dynamic_cast<Student&>( *pClone );
  103.  
  104.     wcout
  105.         << "Name: " << studentRef.name()
  106.         << ". Student id: " << studentRef.studentId() << "."
  107.         << endl;
  108. }
  109.  
Success #stdin #stdout 0.01s 2876KB
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Standard input is empty
stdout
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Name: John Smith. Student id: 12345.
Name: Mary Jones. Student id: 88888.
https://ideone.com/3jllc
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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