Dear all, Yep, again it's me, and it's agian function_traits<>... AFAIK, std::iterator_traits<> is one of the counterparts of function_traits<>, not? A sort of symmetry which iterator_traits<> has got is that it can work for Iterators as well as plain pointers. This seems to be not the case for function_traits<>. That is, you can pass a function type to it, but you can't do that for a functor. Is that right? If it is, a big drawback turns out to happen for variations of the following which are not that few common: template < typename ..., ..., typename Function > struct Foo { typedef typename function_traits<Function> ::result_type result_type; Foo (Function f) : f_(f) {} //... result_type operator () () {/*..*/} Function f_; }; This well works for sth like this: double f(double) {/*...*/} Foo<blah, ..., double (&) (double)> foo(f); But it does not work with the following: struct F { double operator () () {/*...*/} }; Foo f; Foo<blah, ..., F> foo(f); Is this what it should be? Or am I missing anything? In fact, the following code: struct F { double operator () (double x) const {return f(x);} }; typedef boost::function_traits<F>::result_type result_type; makes GCC 3.3.1 to give me an error like the previous one. This is what it says: Compiler: Default compiler Building Makefile: "C:\Documents and Settings\Hossein\My Documents\My Programmes\Probability I\Distributions\7.2.1\Makefile.win" Executing make... make.exe -f "C:\Documents and Settings\Hossein\My Documents\My Programmes\Probability I\Distributions\7.2.1\Makefile.win" all g++.exe -D__DEBUG__ -c 7_2_1Main.cpp -o 7_2_1Main.o -I"C:/Dev-Cpp/include/c++/3.3.1" -I"C:/Dev-Cpp/include/c++/3.3.1/mingw32" -I"C:/Dev-Cpp/include/c++/3.3.1/backward" -I"C:/Dev-Cpp/lib/gcc-lib/mingw32/3.3.1/include" -I"C:/Dev-Cpp/include" -pg -g3 7_2_1Main.cpp: In instantiation of `boost::function_traits<F>': 7_2_1Main.cpp:70: instantiated from `inverse_variate_generator<main()::Engine, main()::Distribution, F>' 7_2_1Main.cpp:106: instantiated from here 7_2_1Main.cpp:70: error: base class `boost::detail::function_traits_helper<F*>' has incomplete type 7_2_1Main.cpp: In instantiation of `inverse_variate_generator<main()::Engine, main()::Distribution, F>': 7_2_1Main.cpp:106: instantiated from here 7_2_1Main.cpp:70: error: no type named `result_type' in `struct boost::function_traits<F>' 7_2_1Main.cpp:76: error: no type named `result_type' in `struct boost::function_traits<F>' 7_2_1Main.cpp: In function `int main()': 7_2_1Main.cpp:113: error: no match for call to `( inverse_variate_generator<main()::Engine, main()::Distribution, F>) ()' 7_2_1Main.cpp:117: error: no match for call to `( inverse_variate_generator<main()::Engine, main()::Distribution, F>) ()' make.exe: *** [7_2_1Main.o] Error 1 Execution terminated What's wrong with it? Am I missing anything? If I'm not missing anything, then what is the work-around? I find myself right in expecting myself to be able to write a functor (like Foo) which can work equaly well with both function pointers and functors, as like as how the Standard algorithms do. Am I right? Or am I right? ;) TIA, --Hossein __________________________________ Do you Yahoo!? Take Yahoo! Mail with you! Get it on your mobile phone. http://mobile.yahoo.com/maildemo