fork(1) download 
  1. // Remove "x" to invoke feature.
  2. #define     xTEST_BAD_ASSIGN
  3.  
  4. #if defined( CPP11 )
  5. #   define OVERRIDE override
  6. #   define NOEXCEPT noexcept
  7. #else
  8. #   define OVERRIDE
  9. #   define NOEXCEPT throw()
  10. #endif
  11.  
  12. //---------------------------------------------------------------------------
  13. #include <algorithm>        // std::swap
  14. #include <iostream>         // std::wcout, std::endl
  15. #include <string>           // std::string
  16. #include <utility>          // std::forward
  17. using namespace std;
  18.  
  19. #if defined( CPP11 )
  20.     template< class Base >
  21.     class Assignable_ final
  22.         : public Base
  23.     {
  24.     public:
  25.         using Base::Base;
  26.         using Base::operator=;
  27.     };
  28. #else
  29.     template< class Base >
  30.     class Assignable_;
  31.  
  32.     class IsFinalAssignable
  33.     {
  34.     template< class > friend class Assignable_;
  35.     private:
  36.         IsFinalAssignable() {}
  37.     };
  38.  
  39.     template< class Base >
  40.     class Assignable_
  41.         : private virtual IsFinalAssignable
  42.         , public Base
  43.     {
  44.     public:
  45.         Assignable_(): Base() {}
  46.  
  47.         template< class Arg1 >
  48.         Assignable_( Arg1 const& a1 )
  49.             : Base( a1 )
  50.         {}
  51.  
  52.         template< class Arg1, class Arg2 >
  53.         Assignable_( Arg1 const& a1, Arg2 const& a2 )
  54.             : Base( a1, a2 )
  55.         {}
  56.  
  57.         using Base::operator=;
  58.     };
  59. #endif
  60.  
  61. class Person
  62. {
  63. private:
  64.     string  name_;
  65.  
  66. protected:
  67.     void swapWith( Person& other ) NOEXCEPT
  68.     {
  69.         swap( name_, other.name_ );
  70.     }
  71.  
  72.     void operator=( Person other ) { swapWith( other ); }
  73.  
  74. public:
  75.     typedef Assignable_<Person> Assignable;
  76.  
  77.     string name() const { return name_; }
  78.  
  79.     Person( string const& name )
  80.         : name_( name )
  81.     {}
  82. };
  83.  
  84. class Student
  85.     : public Person
  86. {
  87. private:
  88.     int     studentId_;
  89.  
  90. protected:
  91.     void swapWith( Student& other ) NOEXCEPT
  92.     {
  93.         Person::swapWith( other );
  94.         swap( studentId_, other.studentId_ );
  95.     }
  96.  
  97.     void operator=( Student other ) { swapWith( other ); }
  98.  
  99. public:
  100.     typedef Assignable_<Student> Assignable;
  101.  
  102.     int studentId() const { return studentId_; }
  103.  
  104.     Student( string const& name, int const studentId )
  105.         : Person( name ), studentId_( studentId )
  106.     {}
  107. };
  108.  
  109. #ifdef TEST_EXTENSION
  110. class Extension
  111.     : public Person::Assignable
  112. {
  113. public:
  114.     Extension(): Person::Assignable( "Somebody" ) {}
  115. };
  116. #endif
  117.  
  118. wostream& operator<<( wostream& stream, string const& s )
  119. {
  120.     return (stream << s.c_str());
  121. }
  122.  
  123. int main()
  124. {
  125.     Person::Assignable      a( "Hillary Clinton" );
  126.     Student::Assignable     b1( "John Smith", 12345 );
  127.     Student                 b2( "Mary Jones", 88888 );
  128.     Person&                 bAsPerson = b1;      // OK.
  129.  
  130.     wcout
  131.         << "Name: " << b1.name()
  132.         << ". Student id: " << b1.studentId() << "."
  133.         << endl;
  134.  
  135. #ifdef TEST_BAD_ASSIGN
  136.     bAsPerson = a;              // Does not compile. :-)
  137. #else
  138.     b1 = b2;                    // Good/allowed assignment.
  139. #endif
  140.  
  141.     wcout
  142.         << "Name: " << b1.name()
  143.         << ". Student id: " << b1.studentId() << "."
  144.         << endl;
  145. }
  146.  
Success #stdin #stdout 0.01s 2876KB
comments (?)
stdin 
Standard input is empty
stdout 
Name: John Smith. Student id: 12345.
Name: Mary Jones. Student id: 88888.
https://ideone.com/T9Kw5
language:
C++ (gcc 8.3)
created:
14 years ago
visibility:
public

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