Re: [boost] Tuples and Bind problem

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-07-13 12:43:53

Arash Partow wrote:
> Hi all,
>
> I'm having some difficulties getting the following piece of code to
> compile:
>
>
> #include <iostream>
> #include <vector>
>
> #include <boost/utility.hpp>
> #include <boost/bind.hpp>
> #include <boost/tuple/tuple.hpp>
>
>
> class AClass
> {
> public:
>    AClass(){}
>    void b(int i, int j, int k)
>    {
>       std:: cout << "a::b() - " << i << "\t" << j << "\t" << k <<
>    std::endl; }
> };
>
> template <typename T,int i> class select
> {
> public:
>   typedef typename boost::tuples::element<i,T>::type result_type;
>
>   template <typename U>
>   result_type operator()(const U& u) const

The simpler

   result_type operator()(const T& u) const

ought to work, too.

>   {
>     return u.get<i>();

You might need u.template get<i>(); here depending on the compiler.

>   }
>
> };
>
> int main(int argc, char* argv[])
> {
>   typedef boost::tuples::tuple<AClass,int,int,int> param_set;
>
>    std::vector<param_set> list;
>    list.push_back(param_set(AClass(),1,2,3));
>    list.push_back(param_set(AClass(),2,3,4));
>    list.push_back(param_set(AClass(),3,4,5));
>    list.push_back(param_set(AClass(),4,5,6));
>    list.push_back(param_set(AClass(),5,6,7));
>
>     std::for_each(
>                   list.begin(),
>                   list.end(),
>                   boost::bind(&AClass::b,
>                               boost::bind(select<param_set,0>(),_0),

There is no placeholder named _0, they start at _1.

>                               boost::bind(select<param_set,0>(),_1),
>                               boost::bind(select<param_set,0>(),_2),
>                               boost::bind(select<param_set,0>(),_3)));

You don't have enough arguments to use _2 or _3 as for_each only passes one. 
Instead of trying to get<0> the first element of the four tuples _0.._3, you 
need to get<0..3> the four elements of the one tuple _1.

                               boost::bind(select<param_set,0>(),_1),
                               boost::bind(select<param_set,1>(),_1),
                               boost::bind(select<param_set,2>(),_1),
                               boost::bind(select<param_set,3>(),_1)));