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  1. #include <memory>
  2. #include <iostream>
  3.  
  4. struct base
  5. {
  6.     using ptr = std::shared_ptr<base> ;
  7.  
  8.     base( int i ) : a(i) {}
  9.     virtual ~base() {}
  10.  
  11.     virtual ptr plus( int i ) const { return std::make_shared<base>( a+i ) ; }
  12.  
  13.     virtual  std::ostream& print( std::ostream& stm ) const
  14.     { return stm << "base{" << a << '}' ; }
  15.  
  16.     int a ;
  17. };
  18.  
  19. struct derived : base
  20. {
  21.     derived( int i, int j ) : base(i), b(j) {}
  22.  
  23.     virtual  ptr plus( int i ) const override
  24.     { return std::make_shared<derived>( a+i, b+i ) ; }
  25.  
  26.     virtual  std::ostream& print( std::ostream& stm ) const
  27.     { return stm << "derived{" << a << ',' << b << '}' ; }
  28.  
  29.     int b ;
  30. };
  31.  
  32. struct surrogate
  33. {
  34.     // in real life, we may need to colour constructors
  35.     surrogate( int i ) : p( std::make_shared<base>(i) ) {}
  36.     surrogate( int i, int j ) : p( std::make_shared<derived>(i,j) ) {}
  37.  
  38.     surrogate( base::ptr pp ) : p(pp) {}
  39.  
  40.     base::ptr p ;
  41. };
  42.  
  43. surrogate operator+ ( const surrogate& s, int i ) { return s.p->plus(i) ; }
  44. surrogate operator+ ( int i, const surrogate& s ) { return s + i ; }
  45. std::ostream& operator<< ( std::ostream& stm, const surrogate& s )
  46. { return s.p->print(stm) ; }
  47.  
  48. int main()
  49. {
  50.     surrogate a(100), b(200,300) ;
  51.     std::cout << "a: " << a << "  a+1234: " << a+1234 << '\n' ;
  52.     std::cout << "b: " << b << "  5678+b: " << 5678+b << '\n' ;
  53. }
  54.  
Success #stdin #stdout 0s 3032KB
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stdin
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Standard input is empty
stdout
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a: base{100}  a+1234: base{1334}
b: derived{200,300}  5678+b: derived{5878,5978}
https://ideone.com/03mN3B
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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