这个问题是我所关心的另一个问题的衍生boost::fusion。这个想法是用来boost::fusion迭代包含 N 维数组的大型 C 风格结构。这些数组的计算由 完成Eigen。通过使用boost::fusion，可以对整个 C 结构应用简单的算术运算，例如标量乘法或向量加法。
在处理二进制操作时，我使用boost::fusion::zip形成单个序列，并boost::fusion::for_each迭代其他序列。
问题boost::fusion::zip在于它const在我需要修改其中一个值（例如加法的返回值）时构造序列。因此，我最终使用const_cast来修改该值（Eigen向量），但由于某种原因，我不能result_ref在add()函数中使用 a 。这是为什么？
此外，有没有更好（或更简单）的方法来实现我想要做的事情？boost::fusion::zip可能不是最合适的，但我找不到任何其他简单的方法来做到这一点。
#include <iostream>
#include <boost/fusion/adapted/struct/adapt_struct.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/algorithm/iteration/for_each.hpp>
#include <boost/fusion/include/for_each.hpp>
#include <boost/fusion/algorithm/transformation/zip.hpp>
#include <boost/fusion/include/zip.hpp>
#include <boost/bind.hpp>
#include <boost/fusion/container/vector/vector30.hpp>
#include <boost/fusion/include/vector30.hpp>
#include <boost/fusion/sequence/intrinsic/at_c.hpp>
#include <boost/fusion/include/at_c.hpp>
#include <boost/type_traits/remove_const.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <Eigen/Core>
template <class type_const_ref>
struct remove_const_ref
{
typedef typename boost::remove_reference <type_const_ref>::type type_const;
typedef typename boost::remove_const <type_const_ref>::type type_ref;
typedef typename boost::remove_const <type_const >::type type;
};
namespace demo
{
template<typename T, int SIZE1, int SIZE2>
struct data
{
T ar1[SIZE1][SIZE2];
T ar2[SIZE1][SIZE2];
};
template<typename T>
struct EigenMap
{
typedef Eigen::Map<Eigen::Matrix<T, Eigen::Dynamic, 1> > type;
};
template<typename T>
struct data_eigen
{
template <int SIZE1, int SIZE2>
data_eigen(data<T,SIZE1,SIZE2>& src)
: ar1(typename EigenMap<T>::type(&src.ar1[0][0], SIZE1*SIZE2)),
ar2(typename EigenMap<T>::type(&src.ar2[0][0], SIZE1*SIZE2))
{
}
typename EigenMap<T>::type ar1;
typename EigenMap<T>::type ar2;
};
struct print
{
template<typename T>
void operator()(const Eigen::Map<Eigen::Matrix<T, Eigen::Dynamic, 1> >& t) const
{
std::cout << t.transpose() << std::endl;
}
};
struct scalarMult
{
template<typename T, typename U>
void operator()(T& t, U& u) const
{
t *= u;
}
};
template <typename T>
struct add
{
template <typename U>
void operator() (const boost::fusion::vector3<U,U,U>& t) const
{
typedef typename remove_const_ref<U>::type_ref vector_ref;
typedef typename remove_const_ref<U>::type vector_type;
// FIXME: find why we cannot use vector_ref
vector_type result_ref = const_cast<vector_ref>(boost::fusion::at_c<2>(t));
result_ref = boost::fusion::at_c<0>(t) + boost::fusion::at_c<1>(t);
}
};
}
BOOST_FUSION_ADAPT_TPL_STRUCT
(
(T),
(demo::data_eigen) (T),
(typename demo::EigenMap<T>::type, ar1)
(typename demo::EigenMap<T>::type, ar2)
)
int main()
{
typedef float REALTYPE;
const int SIZE1 = 2;
const int SIZE2 = 2;
// Basic data structure with multidimensional arrays
demo::data<REALTYPE, SIZE1, SIZE2> d1;
for (unsigned int i = 0; i < SIZE1; ++i)
for (unsigned int j = 0; j < SIZE2; ++j)
{
d1.ar1[i][j] = (i+1)*(j+1);
d1.ar2[i][j] = i + j;
}
demo::data<REALTYPE, SIZE1, SIZE2> d2;
demo::data<REALTYPE, SIZE1, SIZE2> d3;
memset(&d3, 0, sizeof(demo::data<REALTYPE, SIZE1, SIZE2>));
for (unsigned int i = 0; i < SIZE1; ++i)
for (unsigned int j = 0; j < SIZE2; ++j)
{
d2.ar1[i][j] = 1.0;
d2.ar2[i][j] = 2.0;
}
// Eigen::Map + BOOST_FUSION_ADAPT_TPL_STRUCT
demo::data_eigen<REALTYPE> eig_d1(d1);
demo::data_eigen<REALTYPE> eig_d2(d2);
demo::data_eigen<REALTYPE> eig_d3(d3);
std::cout << "d1:" << std::endl;
boost::fusion::for_each(eig_d1, demo::print());
std::cout << std::endl;
std::cout << "d2:" << std::endl;
boost::fusion::for_each(eig_d2, demo::print());
std::cout << std::endl;
boost::fusion::for_each(eig_d1, boost::bind<void>(demo::scalarMult(), _1, 2.0));
std::cout << "d1 = 2 * d1:" << std::endl;
boost::fusion::for_each(eig_d1, demo::print());
std::cout << std::endl;
boost::fusion::for_each(boost::fusion::zip(eig_d1, eig_d2, eig_d3),
demo::add<REALTYPE>());
std::cout << "d3 = d1 + d2:" << std::endl;
boost::fusion::for_each(eig_d3, demo::print());
std::cout << std::endl;
return EXIT_SUCCESS;
}