Re: [Boost-users] [lambda] bind w/shared_ptr<Object> [Was: "Invalid use of void expression"]

David A. Greene wrote:

I'm having some trouble with BLL and Boost.Function in this simple testcase:

I worked around the problem using Boost.Function: int main(void) { Test tester; int value = 10; boost::function bound = boost::lambda::bind(&Test::foo, &tester, boost::lambda::_1); Caller > printer(boost::lambda::bind(bound, value)); //Caller > printer(boost::lambda::bind(boost::lambda::bind(&Test::foo, &tester, boost::lambda::_1), value)); printer.bar(); return(0); } I have a couple of questions and another problem, however. I had to pass "&tester" to the first bind expression because g++ complained about passing "tester" as "const Test &." Is passing by reference supposed to work? Also, this workaround gets rid of the error but is the original code supposed to work as written or did I do something incorrectly? Finally, the new problem, closer to the actual code I'm working with: #include #include #include #include <iostream> class Test { public: void foo(int a) { std::cout << "a is " << a << std::endl; }; }; template<typename Function> class Caller { private: Function func; public: Caller(Function f) : func(f) {}; void bar(void) { func(); }; }; int main(void) { boost::shared_ptr<Test> tester(new Test); int value = 10; boost::function bound = boost::lambda::bind(&Test::foo, tester, boost::lambda::_1); Caller > printer(boost::lambda::bind(bound, value)); printer.bar(); return(0); } g++ comaplains (full trace below): lambda4.cc:28: instantiated from here /usr/include/boost/lambda/detail/actions.hpp:96: error: no matching function for call to 'boost::lambda::function_adaptor::apply(void (Test::* const&)(int), const boost::shared_ptr<Test>&, int&)' /usr/include/boost/lambda/detail/function_adaptors.hpp:245: note: candidates are: static Result boost::lambda::function_adaptor::apply(Result (Object::*)(Arg1), Object*, A1&) [with RET = void, A1 = int, Object = Test, Arg1 = int, Result = void] /usr/include/boost/lambda/detail/function_adaptors.hpp:249: note: static Result boost::lambda::function_adaptor::apply(Result (Object::*)(Arg1), Object&, A1&) [with RET = void, A1 = int, Object = Test, Arg1 = int, Result = void] /usr/include/boost/lambda/detail/actions.hpp:96: error: return-statement with a value, in function returning 'void' Any ideas? I'd rather not use .get() because of the potential deallocation that might happen out from under the bound function. -Dave -------------------- /usr/include/boost/lambda/detail/actions.hpp: In static member function 'static RET boost::lambda::function_action<3, T>::apply(A1&, A2&, A3&) [with RET = void, A1 = void (Test::* const)(int), A2 = const boost::shared_ptr<Test>, A3 = int, T = boost::lambda::detail::unspecified]': /usr/include/boost/lambda/detail/lambda_functor_base.hpp:425: instantiated from 'RET boost::lambda::lambda_functor_base, Args>::call(A&, B&, C&, Env&) const [with RET = void, A = int, B = const boost::tuples::null_type, C = const boost::tuples::null_type, Env = const boost::tuples::null_type, Act = boost::lambda::function_action<3, boost::lambda::detail::unspecified>, Args = boost::tuples::tuple >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type>]' /usr/include/boost/lambda/detail/lambda_functors.hpp:148: instantiated from 'typename T::sig >::type boost::lambda::lambda_functor<Base>::operator()(A&) const [with A = int, T = boost::lambda::lambda_functor_base >, boost::tuples::tuple >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> >]' /usr/include/boost/function/function_template.hpp:136: instantiated from 'static void boost::detail::function::void_function_obj_invoker1::invoke(boost::detail::function::any_pointer, T0) [with FunctionObj = boost::lambda::lambda_functor >, boost::tuples::tuple >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >, R = void, T0 = int]' /usr/include/boost/function/function_template.hpp:479: instantiated from 'void boost::function1::assign_to(FunctionObj, boost::detail::function::function_obj_tag) [with FunctionObj = boost::lambda::lambda_functor >, boost::tuples::tuple >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >, R = void, T0 = int, Allocator = std::allocator<void>]' /usr/include/boost/function/function_template.hpp:430: instantiated from 'void boost::function1::assign_to(Functor) [with Functor = boost::lambda::lambda_functor >, boost::tuples::tuple >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >, R = void, T0 = int, Allocator = std::allocator<void>]' /usr/include/boost/function/function_template.hpp:294: instantiated from 'boost::function1::function1(Functor, typename boost::enable_if_c::value, int>::type) [with Functor = boost::lambda::lambda_functor >, boost::tuples::tuple >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >, R = void, T0 = int, Allocator = std::allocator<void>]' /usr/include/boost/function/function_template.hpp:637: instantiated from 'boost::function::function(Functor, typename boost::enable_if_c::value, int>::type) [with Functor = boost::lambda::lambda_functor >, boost::tuples::tuple >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >, R = void, T0 = int, Allocator = std::allocator<void>]' lambda4.cc:28: instantiated from here /usr/include/boost/lambda/detail/actions.hpp:96: error: no matching function for call to 'boost::lambda::function_adaptor::apply(void (Test::* const&)(int), const boost::shared_ptr<Test>&, int&)' /usr/include/boost/lambda/detail/function_adaptors.hpp:245: note: candidates are: static Result boost::lambda::function_adaptor::apply(Result (Object::*)(Arg1), Object*, A1&) [with RET = void, A1 = int, Object = Test, Arg1 = int, Result = void] /usr/include/boost/lambda/detail/function_adaptors.hpp:249: note: static Result boost::lambda::function_adaptor::apply(Result (Object::*)(Arg1), Object&, A1&) [with RET = void, A1 = int, Object = Test, Arg1 = int, Result = void] /usr/include/boost/lambda/detail/actions.hpp:96: error: return-statement with a value, in function returning 'void'