[ITK-users] Operator overloading in ITK objects.

[Bradley Lowekamp]

Hello,

I think the issue is that the variables pair1 and pair2 are SmartPointers not the derived data object type, so your operators are working on a different object type than you expected.

ITK was not designed for use with overloaded operators with it's data objects and process objects.

You could likely hack it by doing (*pair1) == (*pair2), if you really want to use overloaded operators. Otherwise a conventional member function could just as easily be used.

Brad

On Oct 14, 2014, at 11:31 AM, DVigneault <davis.vigneault at gmail.com> wrote:

> All--
> 
> I've defined an ITK object inheriting from itk::DataObject (full header file
> copied below).  The object has two properties: Index and Value.  I've tried
> to overload the == and < operators (basing my syntax off of itk::Point) so
> that the two objects would be equal if they have the same index, and one
> would be less than the other if one's value is less than the other's:
> 
>  bool operator==(const Self & pt) const {
>    return this->GetIndex() == pt->GetIndex(); }
> 
>  bool operator<(const Self & pt) const {
>    return this->GetValue() < pt->GetValue(); }
> 
> However, the less than operator isn't functioning as intended:
> 
> 	typedef IndexValuePair< IndexType, PixelType > PairType;
> 	typename PairType::Pointer pair1 = PairType::New();
> 	IndexType index1;
> 	pair1->SetIndex( index1.Fill( 0 ) );
> 	pair1->SetValue( 1 );
> 	
> 	typename PairType::Pointer pair2 = PairType::New();
> 	IndexType index2;
> 	pair2->SetIndex( index2.Fill( 1 ) );
> 	pair2->SetValue( 0 );
> 	
> 	std::cout << (pair1 == pair2) << std::endl; // 0
> 	std::cout << (pair1 == pair1) << std::endl; // 1
> 	std::cout << (pair1 < pair2) << std::endl; // 1
> 
> Interestingly, the results do not change if I comment out the overloading
> operators in the header file, or if I change the values of the pairs,
> suggesting that the program is comparing the objects based on some other
> criteria.  Any ideas what I'm doing wrong?  Apologies in advance if this is
> more of a c++ question and less of an ITK question--I'm sometimes not sure
> whether my problem is due to my misunderstanding the language or the
> library.
> 
> Best,
> 
> --Davis
> 
> Best, and thanks,
> 
> --Davis
> 
> *** Header **
> 
> #ifndef __itkIndexValuePair_h
> #define __itkIndexValuePair_h
> 
> #include "itkDataObject.h"
> 
> namespace itk
> {
> 
> template < typename IndexType, typename ValueType >
> class IndexValuePair:public DataObject
> {
> 
> public:
> 
>  /** Standard class typedefs. */
>  typedef IndexValuePair             Self;
>  typedef DataObject                 Superclass;
>  typedef SmartPointer< Self >       Pointer;
>  typedef SmartPointer< const Self > ConstPointer;
> 
>  /** Method for creation through the object factory. */
>  itkNewMacro(Self);
> 
>  /** Standard part of every itk Object. */
>  itkTypeMacro(IndexValuePair, DataObject);
> 
>  itkSetMacro( Index, IndexType );
>  itkGetMacro( Index, IndexType );
> 
>  itkSetMacro( Value, ValueType );
>  itkGetMacro( Value, ValueType );
> 
> 
>  /** Compare two points for equality. */
>  bool
>  operator==(const Self & pt) const
>  {
>    return this->GetIndex() == pt->GetIndex();
>  }
> 
>  /** Less than. */
>  bool
>  operator<(const Self & pt) const
>  {
>    return this->GetValue() < pt->GetValue();
>  }
> 
> protected:
>  /** Constructor for use by New() method. */
>  IndexValuePair() {}
>  ~IndexValuePair() {}
> //   virtual void PrintSelf(std::ostream & os, Indent indent) const;
> 
>  IndexType m_Index;
>  ValueType m_Value;
> 
> private:
>  IndexValuePair(const Self &);       //purposely not implemented
>  void operator=(const Self &); //purposely not implemented
> 
> };
> 
> }
> 
> #endif
> 
> 
> 
> --
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