Hi there, after making what I then thought was a bad mistake, I discovered that the code below actually works (gcc 4.3.1, OpenSUSE 11 64bit, Boost 1.36). I.e., there is an implicit cast from shared_ptr<derived> to shared_ptr<base> to make it fit the function argument, although both represent different types. Is this intended behaviour (i.e. portable) ? I did not find a corresponding description in the docu. Thanks and Best Regards, Ruediger /**************************************************************************/ #include <iostream> #include class base{ public: virtual ~base(){} virtual void print() const { std::cout << "Hello world from base" << std::endl; } }; class derived :public base { public: void print() const { std::cout << "Hello world from derived" << std::endl; } }; void executeBasePrint(const boost::shared_ptr<base>& base_ptr){ base_ptr->print(); } main(){ boost::shared_ptr<derived> derived_ptr(new derived()); // Results in "Hello world from derived" executeBasePrint(derived_ptr); }