Re: [boost] Boost::lambda::call_xxx, right or wrong?

From: Robin.Hu (huxw_at_[hidden])
Date: 2002-12-09 14:11:35

I use the header file <boost/bind.hpp> instead of <boost/lambda/bind.hpp>
by mistake. Thanks for your help.

On Mon, 9 Dec 2002 13:16:38 -0500 (EST)
Jaakko Jarvi <jajarvi_at_[hidden]> wrote:

> The algorithm.hpp header is badly broken in 1.29 (wrong file 
> in the wrong place at the wrong time). This is fixed in the cvs main 
> trunk. 
> 
> The following program compiles and runs fine (with gcc3.2).
> 
> Cheers, Jaakko
> 
> 
> // ------------------
> #include <boost/lambda/lambda.hpp>
> #include <boost/lambda/bind.hpp>
> #include <boost/lambda/algorithm.hpp>
> 
> #include <vector>
> #include <iostream>
> 
> using namespace boost::lambda;
> 
> int main() {
> 
>  std::vector<int> b1;
>  b1.push_back(1); b1.push_back(2);
> 
>  std::vector<int> b2;
>  b2.push_back(3); b2.push_back(4); b2.push_back(5);
> 
>  std::vector<std::vector<int> > a;
>  a.push_back(b1); 
>  a.push_back(b2); 
> 
>  int sum = 0;
>   std::for_each(a.begin(), a.end(),
>      bind(ll::for_each(),
>         bind(call_begin(), _1), bind(call_end(), _1),
>         protect(sum += _1)));
> 
>   std::cout << "sum = " << sum << "\n";
> }
> // ------------------
> 
> 
> 
> 
> On Tue, 10 Dec 2002, Robin.Hu wrote:
> 
> > Hi Boosters:
> > 
> >    In the document of boost::lambda (ar01s05.html#sect:nested_stl_algorithms), 
> > it says:
> > ------------------>cited begin<-------------------
> >    Some aid for common special cases can be provided though. The BLL defines two 
> >    helper function object classes, call_begin and call_end, which wrap a
> >    call to the begin and, respectively, end functions of a container,
> >    and return the const_iterator type of the container. With these
> >    helper templates, the above code becomes: 
> > 
> >    std::for_each(a.begin(), a.end(), 
> >       bind(ll::for_each(), 
> >          bind(call_begin(), _1), bind(call_end(), _1),
> >          protect(sum += _1)));
> > ------------------->cited end<---------------------
> > 
> >    But I failed to compile this example with gcc 3.2 and vc 2003 beta.
> > I think the problem is, both struct call_begin and struct call_end dont
> > provide a result_type. 
> > 
> > [lambda/algorithm.hpp]
> > ------------------->cited begin<-------------------
> > #define CALL_MEMBER(X)                                     \
> > struct call_##X {                                          \
> > template <class Args>                                      \
> >   struct sig {                                             \
> >     typedef typename boost::remove_const<                  \
> >         typename boost::tuples::element<1, Args>::type     \
> >      >::type::const_iterator type;                         \
> >   };                                                       \
> >                                                            \
> >   template<class T>                                        \
> >   typename T::const_iterator                               \
> >   operator()(const T& t) const                             \
> >   {                                                        \
> >     return t.X();                                          \
> >   }                                                        \
> > };
> > ------------------->cited end<---------------------
> >  
> >   Is there anything I missed? And is there a possibel way to make these
> > call_xxx run?
> > 
> > 
> 
> -- 
> --
> -- Jaakko Järvi                       email: jajarvi_at_[hidden]
> -- Post Doctoral Fellow               phone: [phone]
> -- Pervasive Technology Labs          fax:   [phone]
> -- Indiana University, Bloomington
> 
> 
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-- 
 <huxw_at_[hidden]>