CODEWITHSUNDEEP
c++classtemplatesinterfaceeigen
greywolf82
greywolf82

Reputation: 22173

Extending Eigen Ref class

I'm trying to extend the Ref Eigen class in order to use custom classes. I've got the following code:

#include <iostream>
#include <eigen3/Eigen/Dense>

class Interface {
public:
    virtual ~Interface() {
    }
    virtual void customMethod() const = 0;
};

class MyVectorType: public Eigen::Matrix<double, 3, 1, Eigen::DontAlign>,
        public Interface {
public:
    MyVectorType(void) :
            Eigen::Matrix<double, 3, 1, Eigen::DontAlign>() {
    }
    typedef Eigen::Matrix<double, 3, 1, Eigen::DontAlign> Base;
    // This constructor allows you to construct MyVectorType from Eigen expressions
    template<typename OtherDerived>
    MyVectorType(const Eigen::MatrixBase<OtherDerived>& other) :
            Eigen::Matrix<double, 3, 1, Eigen::DontAlign>(other) {
    }
    // This method allows you to assign Eigen expressions to MyVectorType
    template<typename OtherDerived>
    MyVectorType & operator=(const Eigen::MatrixBase<OtherDerived>& other) {
        this->Base::operator=(other);
        return *this;
    }
    virtual void customMethod() const {
        std::cout << rows() << std::endl;
    }
};

template<typename T, int Options>
class MyRef: public Eigen::Ref<typename T::Base, Options, Eigen::Stride<0, 0> >,
        public Interface {
public:
    typedef Eigen::Ref<typename T::Base, Options, Eigen::Stride<0, 0> > Base;
    template<typename Derived>
    MyRef(Eigen::DenseBase<Derived>& expr) :
            Eigen::Ref<typename T::Base, Options, Eigen::Stride<0, 0> >(expr) {
    }
    virtual void customMethod() const {
        std::cout << rows() << std::endl; // <-----error
    }
    EIGEN_INHERIT_ASSIGNMENT_OPERATORS(MyRef)};

template<typename T, int Options>
class MyRef<const T, Options> : public Eigen::Ref<typename T::Base, Options,
        Eigen::Stride<0, 0> >, public Interface {
public:
    template<typename Derived>
    MyRef(const Eigen::DenseBase<Derived>& expr) :
            Eigen::Ref<typename T::Base, Options, Eigen::Stride<0, 0> >(expr) {
    }
    virtual void customMethod() const {
        std::cout << rows() << std::endl; // <-----error
    }
};

void init(MyRef<MyVectorType, Eigen::Unaligned> m) {
    m.customMethod();
}

int main() {
    Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic, Eigen::AutoAlign, 12,
            12> mm(3, 1);
    Eigen::Map<MyVectorType::Base> map(mm.data(), 3, 1);
    MyRef<MyVectorType, Eigen::Unaligned> ref(map);
    init(ref);
    std::cout << mm << std::endl;
    return 0;
}

In order to call custom methods like the method init(), the same interface must be used between MyVectorType and MyRef. So I thought to use an Interface class.

The problem: This code doesn't compile because I can't call rows() inside MyRef, so I don't understand how to access to MyVectorType or the underlying data in Ref class to call other methods.

I tried with derived() to access but it doesn't work. I looked at the source code but I don't understand how Ref can be used normally with all interface of DenseBase. I'd like to do the same thing for my custom methods.

Gcc error:

../main.cpp:49:16: error: there are no arguments to ‘rows’ that depend on a template parameter, so a declaration of ‘rows’ must be available [-fpermissive]
   std::cout << rows() << std::endl;
                ^~~~
../main.cpp:49:16: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)
../main.cpp: In member function ‘virtual void MyRef<const T, Options>::customMethod() const’:
../main.cpp:63:16: error: there are no arguments to ‘rows’ that depend on a template parameter, so a declaration of ‘rows’ must be available [-fpermissive]
   std::cout << rows() << std::endl;
                ^~~~

Upvotes: 4

Views: 271

Answers (1)

JeJo
JeJo

Reputation: 32732

When a Base class depends upon the template parameters, even though Derived (let's say) member_base inherited from the Base, using simply member_base in Derived class, is not equivalent to this->member_base.

That is 

template<typename T>
class Base { public:    void member_base(); };

template<typename T>
class Derived : Base<T> 
{
public:
    void member_derived() 
    {
        member_base(); // calls external(global) member_base() or error
    }
};

In your case, what happend to rows() is exactly same as above case.

You need to qualify using either this-> or Base<T>::, for all members what you inherited from Base .

In your case 

this->row()

or

Eigen::Ref<typename T::Base, Options, Eigen::Stride<0, 0> >::rows()

Upvotes: 3

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