Re: Ill-formed C++0x code or compiler bug (GCC) ?

SG <>
Fri, 28 Jan 2011 17:52:21 -0800 (PST)
On 28 Jan., 20:19, Dilip wrote:

On Jan 28, 5:36 am, SG wrote:

   struct use_copy_ctor {};
   struct prefer_clone_func : use_copy_ctor {};

   template<class T>
   auto clone(T const* ptr, prefer_clone_func)
   -> decltype(ptr->clone())
   { return ptr->clone(); }

   template<class T>
   auto clone(T const* ptr, use_copy_ctor)
   -> decltype(new T(*ptr))
   { return new T(*ptr); }

   struct abc {
     virtual ~abc() {}
     virtual abc* clone() const =0;

   struct derived : abc
     derived* clone() const { return new derived(*this); }

   int main()
     derived d;
     abc* p = &d;
     abc* q = clone(p,prefer_clone_func());
     delete q;

VC++ 2010 fails with a *linker* error:

error LNK2019: unresolved external symbol "public: __thiscall
abc::abc(void)" (??0abc@@QAE@XZ) referenced in function "public:
__thiscall derived::derived(void)" (??0derived@@QAE@XZ)

That's weird. Looks like VC++ forgot to emit the definition of the
"compiler-generated" default constructor of abc.

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