[Boost-users] boost::bind, boost::function & placeholders flexibility

From: jbd (evadream.mlist_at_[hidden])
Date: 2006-05-12 08:05:56

Hello everybody,

First of all, i'm a beginner trying to understand the use of the
boost::bind library. Here is my problem :

I'd like to know if there is a way to omit placeholders when calling
boost::bind and let the compiler deduce their number. I understand that
this is contrary to the flexibility offers by the placeholder, but i need
to do something like that.

void bar() {}
void bar2(int) {}

// Compile and works well
boost::function < void ()> f1( boost::bind(&bar) ) ;
boost::function < void (int) > f2( boost::bind(&bar2,_1) ) ;

// i'd like to write this, but it doesn't compile
// without the placeholders
boost::function < void (int) > f2( boost::bind(&bar2) ) ;

// i can write a small helper function mybind to achieve my goal
// this compile and works well

mybind(bar2) ;

with
        
template <typename Ret, typename Arg1, typename Arg2>
void mybind(Ret (*Func)(Arg1, Arg2))
{
                boost::function<Ret (Arg1, Arg2)> f(Func) ;
}
     
I hope you understand what i've try to show. Maybe i missed something in
the documentation.

Thank you for reading !

Here is the working .cpp file  i use to test
things.

===============================

#include <iostream>
#include <stdexcept>
#include <boost/bind.hpp>
#include <boost/function.hpp>

template <typename Ret, typename Arg1, typename Arg2>
void mybind(Ret (*Func)(Arg1))
{
    boost::function<Ret (Arg1)> f(Func) ;
}

void bar()
{
    std::cout << "bar()\n" ;
}

void bar2(int a)
{
    std::cout << "bar2(int)\n" ;
}

int main (int argc, char* argv[])
{
    try
    {
        // Compile and works well
        {
            boost::function < void ()> f1( boost::bind(&bar) ) ;
            boost::function < void (int) > f2( boost::bind(&bar2,_1) ) ;
        }

        /*
        // i'd like to write this, but it doesn't compile
        {
            // without the placeholders
            boost::function < void (int) > f2( boost::bind(&bar2) ) ;
            f2(5) ;
        }
        */

        // i can write a small helper function mybind to achieve my goal
        // this compile and works well
        /*
        template <typename Ret, typename Arg1, typename Arg2>
        void mybind(Ret (*Func)(Arg1, Arg2))
        {
                boost::function<Ret (Arg1, Arg2)> f(Func) ;
        }
        */
        {
            mybind(bar2) ;
        }
    }
    catch(std::exception& e)
    {
        std::cout << e.what() << '\n' ;
        return -1 ;
    }
    catch(...)
    {
        std::cout << "Non standard exception\n" ;
        return -1 ;
    }
}

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