使用 CWiseNullaryOp 扩展特征:无法重现示例

我正在尝试重现 Eigen 文档此页面上的第二个示例，但无法编译我的最小程序。我正在使用特征 3.3~beta1-2。

当使用以下参数运行 g++ 时-std=c++11 -Wall -pipe -O3 -ffast-math -funsafe-math-optimizations -march=native -mtune=native -pedantic -Wno-unused-variable -I/usr/local/include/eigen3 -I/usr/include/eigen3 -c example.cpp，我收到此错误：

example.cpp:8:41 ("Eigen::MatrixXi B = indexing(A, ri, ci)" in program below)  
/usr/include/eigen3/Eigen/src/Core/CoreEvaluators.h:348:27: error: no match for call to '(const indexing_functor<Eigen::Matrix<int, -1, -1>, Eigen::Array<int, 3, 1>, Eigen::Array<int, -1, 1> >) (Eigen::Index&)
return m_functor(index);

我的最小程序包括以下内容(基本上是从文档中的示例复制和粘贴)：

例子.h

#include <iostream>
#include <stdio.h>
#include <Eigen/Core>
using namespace Eigen;
template<class ArgType, class RowIndexType, class ColIndexType>
class indexing_functor {
const ArgType &m_arg;
const RowIndexType &m_rowIndices;
const ColIndexType &m_colIndices;
public:
typedef Matrix<typename ArgType::Scalar,
RowIndexType::SizeAtCompileTime,
ColIndexType::SizeAtCompileTime,
ArgType::Flags&RowMajorBit?RowMajor:ColMajor,
RowIndexType::MaxSizeAtCompileTime,
ColIndexType::MaxSizeAtCompileTime> MatrixType;
indexing_functor(const ArgType& arg, const RowIndexType& row_indices, const ColIndexType& col_indices)
: m_arg(arg), m_rowIndices(row_indices), m_colIndices(col_indices)
{}
const typename ArgType::Scalar& operator() (Index row, Index col) const {
return m_arg(m_rowIndices[row], m_colIndices[col]);
}
};
template <class ArgType, class RowIndexType, class ColIndexType>
CwiseNullaryOp<indexing_functor<ArgType,RowIndexType,ColIndexType>, typename indexing_functor<ArgType,RowIndexType,ColIndexType>::MatrixType>
indexing(const Eigen::MatrixBase<ArgType>& arg, const RowIndexType& row_indices, const ColIndexType& col_indices)
{
typedef indexing_functor<ArgType,RowIndexType,ColIndexType> Func;
typedef typename Func::MatrixType MatrixType;
return MatrixType::NullaryExpr(row_indices.size(), col_indices.size(), Func(arg.derived(), row_indices, col_indices));
}

示例.cpp

#include "example.h"
int main()
{
Eigen::MatrixXi A = Eigen::MatrixXi::Random(4,4);
Array3i ri(1,2,1);
ArrayXi ci(6); ci << 3,2,1,0,0,2;
Eigen::MatrixXi B = indexing(A, ri, ci);
std::cout << "A =" << std::endl;
std::cout << A << std::endl << std::endl;
std::cout << "A([" << ri.transpose() << "], [" << ci.transpose() << "]) =" << std::endl;
std::cout << B << std::endl;
}

我是否缺少有关模板在C++中如何工作的基本内容？