Ok, thank you responding me ! My example was just here as "proof" of what i need. My idea is to encapsulate a boost::function of any type in a template class, which herite from a pure virtual class FooVirtual. My goal is to transform any function into a FooVirtual* using an helper function. I realize my last message was not very clear, here is a better example #include <iostream> #include <stdexcept> #include #include template boost::function mybind(Ret (*Func)(Arg1)) { boost::function f(Func) ; return f ; } void bar() {} void bar2(int a) {} int main (int argc, char* argv[]) { try { boost::function < void ()> f1( boost::bind(&bar) ) ; boost::function < void (int) > f2( boost::bind(&bar2,_1) ) ; // doesn't work : // boost::function < void (int) > f2( boost::bind(&bar2) ) ; // this is ok boost::function < void (int) > f3( mybind(&bar2) ) ; } catch(std::exception& e) { std::cout << e.what() << '\n' ; return -1 ; } catch(...) { std::cout << "Non standard exception\n" ; return -1 ; } }

Hello,

Peter Dimov wrote: It isn't clear why do you need to bind bar2 at all, instead of just using boost::function < void (int) > f3( &bar2 ) ;

To make a long story short, i'd like people always use the same mecanism (syntax), not a boost::bind here and nothing there. Maybe I tried to simplify my problem too much. The small code i'm "working" on is at the end of this message. I will try to say what i really want to do with words. The idea : class FunctionInterface : -> a pure virtual classe with an public void execute(const std::string&) = 0 member class GeneralFunctor : -> a class with a boost::shared_ptr<FunctionInterface> function_ member which is called via the operator()(const std::string) const ; The constructor take a pointer to a FunctionInterface. template < typename Func > class Functor : public FunctionInterface -> keeps a boost::function<Func> as a member and implement the execute function template < typename FuncType > GeneralFunctor MakeFunctor(FuncType func) -> This is my helper function to build a GeneralFunctor from any boost::function Here is some example : GeneralFunctor f1( MakeFunctor( boost::bind(&bar) ) ) ; GeneralFunctor f2( MakeFunctor( boost::bind(&bar2,_1) ) ) ; But i'd like to write for the convenience of the user and save some typing : GeneralFunctor f2( MakeFunctor( boost::bind(&bar2) ) ) ; But why do i need to use boost::bind here ? Why not directy a boost::function like you suggest to me ? Something like GeneralFunctor f3( MakeFunctor( boost::function(&bar2) ) ) ; As i said, i don't want people (me ;)) asking themself what they should do in this or this situation. That's why i introduce my helper function, mybind, which i can use like that : template boost::function mybind(Ret (*Func)(Arg1)) { boost::function f(Func) ; return f ; } GeneralFunctor f4( MakeFunctor( mybind(bar2) ) ) ; I really can always call MakeFunctor with a boost::function directly, something like MakeFunctor( boost::function(&bar2) ) But my purpose is just to make my life easier by using a uniform way letting boost::bind, or a plenty of overloaded mybind function, doing all the work :D I'd like not to fill the boost::function template parameters myself each time. My message is certainly quite confuse, i'm sorry for that but it certainly show that i don't know well the subject ... and the english language =) Thank you anyway. =========================== #include <iostream> #include <string> #include <stdexcept> #include #include #include class FunctionInterface { public: typedef boost::shared_ptr<FunctionInterface> pointer ; virtual ~FunctionInterface() {} virtual std::string execute(const std::string& params="") const = 0 ; } ; template < typename Func > class Functor : public FunctionInterface { private: typedef Func func_type ; func_type func_ ; public: Functor(Func f) : func_(f) {} std::string execute(const std::string& params="") const { return "" ; } } ; class GeneralFunctor { public: GeneralFunctor(const FunctionInterface::pointer func) : function_(func) {} std::string operator ()(const std::string& params = "") const { if ( !function_ ) throw "Error calling null function pointer" ; return function_->execute(params) ; } private: boost::shared_ptr<FunctionInterface> function_ ; } ; template < typename FuncType > GeneralFunctor MakeFunctor(FuncType func) { FunctionInterface::pointer ptr(new Functor<FuncType>(func)) ; return GeneralFunctor(ptr) ; } template boost::function mybind(Ret (*Func)(Arg1)) { boost::function f(Func) ; return f ; } void bar() {} void bar2(int a) {} int main (int argc, char* argv[]) { try { GeneralFunctor f1( MakeFunctor( boost::bind(&bar) ) ) ; GeneralFunctor f2( MakeFunctor( boost::bind(&bar2,_1) ) ) ; GeneralFunctor f3( MakeFunctor( boost::function(&bar2) ) ) ; GeneralFunctor f4( MakeFunctor( mybind(bar2) ) ) ; } catch(std::exception& e) { std::cout << e.what() << '\n' ; return -1 ; } catch(...) { std::cout << "Non standard exception\n" ; return -1 ; } } =========================== Le Fri, 12 May 2006 22:18:57 +0300, Peter Dimov a écrit :

jbd wrote:

...

template boost::function mybind(Ret (*Func)(Arg1)) { boost::function f(Func) ; return f ; }

[...]

...

// doesn't work : // boost::function < void (int) > f2( boost::bind(&bar2) ) ;

// this is ok boost::function < void (int) > f3( mybind(&bar2) ) ;

It isn't clear why do you need to bind bar2 at all, instead of just using

boost::function < void (int) > f3( &bar2 ) ;

I see your point and i agree with you. My goal is not to build a "pattern" i will use everyday. I'm just learning, testing things =) Thank you for your response ! Le Fri, 12 May 2006 17:46:04 -0400, Arkadiy Vertleyb a écrit :

"jbd" wrote

...

...

Peter Dimov wrote: It isn't clear why do you need to bind bar2 at all, instead of just using boost::function < void (int) > f3( &bar2 ) ;

To make a long story short, i'd like people always use the same mecanism (syntax), not a boost::bind here and nothing there.

I would disagree with this approach. First it introduces unnecessary runtime and compile time performance overhead. More importantly, as great as boost::bind is, it is just a mechanism for making function objects. There are other mechanisms, like, for example, STL binders and adapters, boost::lambda or writing your own function object. A function pointer can be used directly, since function objects are modeled after it in the first place.

Using boost::bind when it is not required might produce the code that is more difficult to understand and maintain.

Regards, Arkadiy

Thank you for those pertinents remarks, i agree perfectly. I just want to train myself by investigating things. My wish is not to invent something i'm gonna be using everyday, only in my 100 lines main.cpp files ;)

At first glance this looks like a very complicated and expensive way of adding an OO layer over boost::function, which is *already* providing all the dynamic polymorphism you need. I could be missing something, but maybe you just need to get comfortable with using boost::function and operator() instead of GeneralFunctor and execute()? FWIW, there's a reason we do this stuff with operator(): it improves interoperability (e.g. with STL).

HTH,