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  1. #include <iostream>
  2. #include <unordered_set>
  3.  
  4. template < typename T > struct magic
  5. {
  6.     magic() { objects.insert( static_cast<T*>(this) ) ; }
  7.     magic( const magic& ) : magic() {}
  8.     magic( magic&& ) : magic() {}
  9.     ~magic() { objects.erase( static_cast<T*>(this) ) ; }
  10.  
  11.     template< typename FN > static void for_each_instance( FN fn )
  12.     { for( T* p : objects ) fn(p) ; }
  13.  
  14.     static std::unordered_set<T*> objects ;
  15. };
  16.  
  17. template < typename T > std::unordered_set<T*> magic<T>::objects ;
  18.  
  19. struct A : magic<A>
  20. {
  21.     void foo( int i, char c )
  22.     { std::cout << "A::foo( " << this << ", " << i << ", " << c << " )\n" ; }
  23. };
  24.  
  25. struct B : magic<B>
  26. {
  27.     void bar( double d ) const
  28.     { std::cout << "B::bar( " << this << ", " << d << " )\n" ; }
  29. };
  30.  
  31. int main()
  32. {
  33.     A one ;
  34.     B two ;
  35.     {
  36.         A three = one ;
  37.         B b[2] ;
  38.         A::for_each_instance( []( A* p ) { p->foo( 99, 'X' ) ; } ) ;
  39.         B::for_each_instance( []( B* p ) { p->bar( 12.8 ) ; } ) ;
  40.     }
  41.     std::cout << "------------------------\n" ;
  42.     A::for_each_instance( []( A* p ) { p->foo( -7, 'Y' ) ; } ) ;
  43.     B::for_each_instance( []( B* p ) { p->bar( 123.45 ) ; } ) ;
  44. }
  45.  
Success #stdin #stdout 0s 2992KB
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stdin
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Standard input is empty
stdout
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A::foo( 0xbfaa5073, 99, X )
A::foo( 0xbfaa5071, 99, X )
B::bar( 0xbfaa5077, 12.8 )
B::bar( 0xbfaa5076, 12.8 )
B::bar( 0xbfaa5072, 12.8 )
------------------------
A::foo( 0xbfaa5071, -7, Y )
B::bar( 0xbfaa5072, 123.45 )
https://ideone.com/9Z2qNR
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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