Quote:Original post by Nypyren
If I had to implement dynamic_cast in a compiler, I'd just CMP the object's vtable pointer to the compiler-known vtable pointer for the type in question, return the object if they match or NULL otherwise.

class A { public: virtual ~A(); };class B : public A {};class C : public B { virtual void next(); };B *Downcast(A* src){    return dynamic_cast<B*>(src);}void go(){    C *c = new C;    B *b = Downcast(C);}

Quote:Original post by Helter Skelter

Quote:Original post by Nypyren
If I had to implement dynamic_cast in a compiler, I'd just CMP the object's vtable pointer to the compiler-known vtable pointer for the type in question, return the object if they match or NULL otherwise.

Unfortunately that won't work in the following situation.

struct A { virtual void make_me_polymorphic() {} };struct B : A {};struct C : B {};int main () {    C exampleC;    C * c = &exampleC;    B * b = dynamic_cast< B * >( c ); //whoops, *c == typeof(C) not typeof(B)    A * a = b; //this works, dynamic_cast should in a similar situation too.    a = &exampleC; //*a == typeof(C)    b = dynamic_cast< B * >( a ); //whoops, *a == typeof(C) not typeof(B)    c = dynamic_cast< C * >( a ); //why should this work but not the above line?}

Quote:Original post by MaulingMonkey
Throw in multiple and virtual inheritence and things can get pretty complicated :-). The actual address pointed to can end up changing!!!