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  1. // http://stackoverflow.com/questions/31878000/static-assertion-that-a-base-pointer-equals-a-derived-pointer
  2.  
  3. template<typename D, typename B>
  4. struct CheckCasting { 
  5.     static D d_static;
  6.  
  7.     constexpr
  8.     static B* bp = &d_static; // the original object is D,
  9.                               // that allows us to static_cast both ways
  10.  
  11.     static
  12.     constexpr bool static_equals_reinterpret() { 
  13.         return static_cast<void*>(static_cast<D*>(bp)) 
  14.             == static_cast<void*>(                bp );
  15.     } 
  16. };
  17.  
  18. struct Base { 
  19.     constexpr Base() : i(0) {}
  20.     int i;
  21. };
  22.  
  23. struct derived_with_virtual : public Base { 
  24.     derived_with_virtual() {}
  25.     virtual void foo() { } 
  26. };
  27. struct without_virtual : public Base { 
  28.     without_virtual() {}
  29. };
  30.  
  31. static_assert( ! CheckCasting<derived_with_virtual, Base> :: static_equals_reinterpret()   ,"");
  32. static_assert(   CheckCasting<without_virtual     , Base> :: static_equals_reinterpret()   ,"");
  33.  
  34. int main() { 
  35. }
  36.  
Success #stdin #stdout 0s 3452KB
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https://ideone.com/ReqjSO
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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