I came across a difference in behavior for Boost.Function between g++ 4.2 and 4.3, and I was wondering whether my usage was incorrect. I'm using default parameters in much the same way as the sample test.cc below. It compiles on 4.2, and does not on 4.3. I think I can see why perhaps it shouldn't have worked, but I'm just looking for a security blanket. If my usage is wrong, it might be worth a mention in the docs, since (to me) either answer is non-intuitive. g++-4.2 4.2.4 (4.2.4-3ubuntu4) g++-4.3 4.3.2 (4.3.2-1ubuntu11) boost 1.35 (1.35.0-8ubuntu1) cat << EOF > test.cc #include <iostream> #include <boost/function.hpp> struct add1 { int operator()(int x, int y = 1) const { return x + y; } }; int add2(int x, int y = 1) { return x + y; } int main() { boost::function <int (int x)> adder1 = add1(); boost::function <int (int x)> adder2 = add2; // compile error here std::cout << adder1(1) << adder2(1) << std::endl; return 0; } EOF mike@hyperion:~> g++-4.2 -Wall -Wextra test.cc -o test && ./test 22 mike@hyperion:~> g++-4.3 -Wall -Wextra test.cc -o test && ./test /usr/include/boost/function/function_template.hpp: In static member function 'static R boost::detail::function::function_invoker1<FunctionPtr, R, T0>::invoke(boost::detail::function::function_buffer&, T0) [with FunctionPtr = int (*)(int, int), R = int, T0 = int]': /usr/include/boost/function/function_template.hpp:787: instantiated from 'void boost::function1<R, T0, Allocator>::assign_to(const Functor&) [with Functor = int (*)(int, int), R = int, T0 = int, Allocator = std::allocator<void>]' /usr/include/boost/function/function_template.hpp:624: instantiated from 'boost::function1<R, T0, Allocator>::function1(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = int (*)(int, int), R = int, T0 = int, Allocator = std::allocator<void>]' /usr/include/boost/function/function_template.hpp:886: instantiated from 'boost::function<R ()(T0), Allocator>::function(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = int (*)(int, int), R = int, T0 = int, Allocator = std::allocator<void>]' test.cc:13: instantiated from here /usr/include/boost/function/function_template.hpp:100: error: too few arguments to function