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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 Cloneable
  27. {
  28. private:
  29.     virtual Cloneable* virtualClone() const = 0;
  30. protected:
  31.     virtual ~Cloneable() {}
  32. };
  33.  
  34. template< class DerivedClass, class BaseClass >
  35. class WithCloningOf_
  36.     : public BaseClass
  37. {
  38. private:
  39.     WithCloningOf_& operator=( WithCloningOf_ const& ) IS_DELETED;
  40.  
  41.     virtual WithCloningOf_* virtualClone() const
  42.     {
  43.         assert( typeid( *this ) == typeid( DerivedClass ) );
  44.         return new DerivedClass( *static_cast<DerivedClass const*>( this ) );
  45.     }
  46.  
  47.     DerivedClass* derivedClassClone() const
  48.     {
  49.         return static_cast<DerivedClass*>( virtualClone() );
  50.     }
  51.  
  52. public:
  53.     typename Ownership<DerivedClass>::Ptr clone() const
  54.     {
  55.         return typename Ownership<DerivedClass>::Ptr( derivedClassClone() );
  56.     }
  57.  
  58.     WithCloningOf_(): BaseClass() {}
  59.  
  60.     template< class Arg1 >
  61.     WithCloningOf_( Arg1 const& a1 )
  62.         : BaseClass( a1 )
  63.     {}
  64.  
  65.     template< class Arg1, class Arg2 >
  66.     WithCloningOf_( Arg1 const& a1, Arg2 const& a2 )
  67.         : BaseClass( a1, a2 )
  68.     {}
  69. };
  70.  
  71. class Person
  72.     : public WithCloningOf_<Person, Cloneable>
  73. {
  74. typedef WithCloningOf_<Person, Cloneable> Base;
  75. private:
  76.     string  name_;
  77.  
  78.     Person& operator=( Person const& ) IS_DELETED;
  79.  
  80. public:
  81.     string name() const { return name_; }
  82.  
  83.     Person( string const& name )
  84.         : name_( name )
  85.     {}
  86. };
  87.  
  88. class Student
  89.     : public WithCloningOf_<Student, Person>
  90. {
  91. typedef WithCloningOf_<Student, Person> Base;
  92. private:
  93.     int     studentId_;
  94.  
  95.     Student& operator=( Student const& ) IS_DELETED;
  96.  
  97. public:
  98.     int studentId() const { return studentId_; }
  99.  
  100.     Student( string const& name, int const studentId )
  101.         : Base( name ), studentId_( studentId )
  102.     {}
  103. };
  104.  
  105. wostream& operator<<( wostream& stream, string const& s )
  106. {
  107.     return (stream << s.c_str());
  108. }
  109.  
  110. int main()
  111. {
  112.     Person                  a( "Hillary Clinton" );
  113.     Student                 b1( "John Smith", 12345 );
  114.     Student                 b2( "Mary Jones", 88888 );
  115.     Person&                 bAsPerson = b1;      // OK.
  116.     Ownership<Person>::Ptr  pClone;
  117.  
  118.     wcout
  119.         << "Name: " << b1.name()
  120.         << ". Student id: " << b1.studentId() << "."
  121.         << endl;
  122.  
  123. #ifdef TEST_ABSTRACT_CLONE
  124.     pClone = bAsPerson.clone(); // OK, clones John Smith the Student.
  125. #else
  126.     pClone = b2.clone();        // More obviously (?) OK, clones Mary.
  127. #endif
  128.     Student& studentRef = dynamic_cast<Student&>( *pClone );
  129.  
  130.     wcout
  131.         << "Name: " << studentRef.name()
  132.         << ". Student id: " << studentRef.studentId() << "."
  133.         << endl;
  134. }
  135.  
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/Coq51
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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