Hello, I have written an adaptor for functions and function objects which allows to invoke operations on the pointees when working on a collection of pointers. For example, it allows to sort a list of pointers by a predicate applying to the pointees. To make it work with normal functions and functors, I utilized boost::unary_traits and boost::binary_traits. This is the class template for the unary version: template< typename Operation > class indirecter_unary : public std::unary_function< typename boost::unary_traits<Operation>::argument_type, typename boost::unary_traits<Operation>::result_type > { typedef typename boost::unary_traits<Operation>::argument_type arg_type; typedef typename boost::unary_traits<Operation>::param_type param_type; typedef typename boost::unary_traits<Operation>::result_type result_type; typedef typename boost::unary_traits<Operation>::function_type function_type; function_type op_; public: explicit indirecter_unary( param_type op ): op_(op) {} result_type operator() (arg_type *arg) const { return op_(*arg); } }; Now, the problem arises when I pass a function which takes references. Like this: bool pred( int& a ) { //... } indirecter_unary< bool ()(int&) > fctor(pred); ext::indirecter_unary<bool ()(int&)>': code/FileBrowser.cpp:90: instantiated from here code/ext/indirect.hpp:80: error: forming pointer to reference type `int&' Line 80 is the line where operator() is defined. The error message indicates that argument_type is obviously not correct in this context. I thought the boost traits would take care of the right argument types? Am I missing something? -- Matthias Kaeppler