I don't understand why the following program doesn't compile when using smart_ptr but works fine with raw pointers: #include <boost/shared_ptr.hpp> class Base { public: virtual ~Base() {}; }; class Base1 : public Base { public: virtual ~Base1() {}; }; class Base2 : public Base { public: virtual ~Base2() {}; }; class Derived1 : public Base1 {}; class Derived2 : public Base2 {}; typedef boost::shared_ptr<Base> BasePtr; typedef boost::shared_ptr<Base1> Base1Ptr; typedef boost::shared_ptr<Base2> Base2Ptr; typedef boost::shared_ptr<Derived1> Derived1Ptr; typedef boost::shared_ptr<Derived2> Derived2Ptr; void f(BasePtr ptr) {} void f(Base1Ptr ptr) {} void f(Base2Ptr ptr) {} int main() { Derived1Ptr d1(new Derived1); Derived2Ptr d2(new Derived2); f(d1); f(d2); } I see the following compile errors with GCC 3.4.4: smart-test.cpp: In function `int main()': smart-test.cpp:24: error: call of overloaded `f(Derived1Ptr&)' is ambiguous smart-test.cpp:15: note: candidates are: void f(BasePtr) smart-test.cpp:16: note: void f(Base1Ptr) smart-test.cpp:17: note: void f(Base2Ptr) smart-test.cpp:25: error: call of overloaded `f(Derived2Ptr&)' is ambiguous smart-test.cpp:15: note: candidates are: void f(BasePtr) smart-test.cpp:16: note: void f(Base1Ptr) smart-test.cpp:17: note: void f(Base2Ptr) If I remove the extra layer of inheritance it works as it should. #include <boost/shared_ptr.hpp> class Base { public: virtual ~Base() {}; }; class Derived1 : public Base {}; class Derived2 : public Base {}; typedef boost::shared_ptr<Base> BasePtr; typedef boost::shared_ptr<Derived1> Derived1Ptr; typedef boost::shared_ptr<Derived2> Derived2Ptr; void f(BasePtr ptr) {} int main() { Derived1Ptr d1(new Derived1); Derived2Ptr d2(new Derived2); f(d1); f(d2); } As I said earlier, doing the same with raw pointers resolves things as would be expected in both cases. Any ideas? --Steven