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

From: Jaakko Jarvi (jajarvi_at_[hidden])
Date: 2002-12-09 13:16:38

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