[Insight-developers] Need help fixing PostOrderTreeIterator type errors!

[Williams, Norman K]

This makes no sense to me after fiddling around with it for a couple of
hours, so I'm asking for help.

There is this bug report: http://www.itk.org/Bug/view.php?id=7455

Consider this test program:
#include "itkSpatialObject.h"
#include "itkSpatialObjectTreeContainer.h"
#include "itkPostOrderTreeIterator.h"

int
itkSpatialObjectTreeContainerIteratorTest(int ac, char *av[])
{
  typedef itk::SpatialObjectTreeContainer<3>     SOTreeType;
  typedef itk::PostOrderTreeIterator<SOTreeType> PostOrderItType;

  SOTreeType::Pointer tree = SOTreeType::New();

  PostOrderItType it(tree);
  return EXIT_SUCCESS;
}



Basically if you try to use a PostOrderTreeIterator with a
SpatialObjectTreeContainer, you get compile errors (see at end of message).


The problem is subtle, and difficult for me to see how to fix:

itkSpatialObjectTreeContainer defines TreeNodeType as
  typedef SpatialObjectTreeNode< TDimension >      TreeNodeType;

but its parent class, TreeContainer defines TreeNodeType as

  typedef TreeNode< ValueType >           TreeNodeType;


The problem is that PostOrderTreeIterator<SpatialObjectTreeContainer<3> >
assumes that TreeContainer::TreeNodeType and
SpatialObjectTreeNodeContainer::TreeNodeType are assignment compatible.

Unfortunately C++ compilers (in my case g++-4.2.1) don't agree.

I've tried a couple of workarounds, but the only thing that seems to work
without causing test regressions is to use reinterpret_cast, which is the
solution of last resort.

I've pushed a patch to Gerrit that fixes the problem, but I think there
must be
a more elegant way to fix the issue.
PATCH: http://review.source.kitware.com/#change,1939

COMPILER ERRORS:

Building CXX object
Modules/Core/SpatialObjects/test/CMakeFiles/ITK-SpatialObjectsTestDriver.di
r/itkSpatialObjectTreeContainerIteratorTest.cxx.o
Modules/Core/Common/include/itkPostOrderTreeIterator.h: In constructor
'itk::PostOrderTreeIterator<TTreeType>::PostOrderTreeIterator(TTreeType*)
[with TTreeType = itk::SpatialObjectTreeContainer<3u>]':
Modules/Core/SpatialObjects/test/itkSpatialObjectTreeContainerIteratorTest.
cxx:36:   instantiated from here
Modules/Core/Common/include/itkPostOrderTreeIterator.h:68: error: invalid
conversion from 'itk::TreeNode<itk::SpatialObject<3u>*>*' to
'itk::SpatialObjectTreeNode<3u>*'
Modules/Core/Common/include/itkPostOrderTreeIterator.h: In member function
'const typename itk::PostOrderTreeIterator<TTreeType>::TreeNodeType*
itk::PostOrderTreeIterator<TTreeType>::FindMostRightLeaf(typename
itk::TreeIteratorBase<TTreeType>::TreeNodeType*) const [with TTreeType =
itk::SpatialObjectTreeContainer<3u>]':
Modules/Core/Common/include/itkPostOrderTreeIterator.h:76:   instantiated
from
'itk::PostOrderTreeIterator<TTreeType>::PostOrderTreeIterator(TTreeType*)
[with TTreeType = itk::SpatialObjectTreeContainer<3u>]'
Modules/Core/SpatialObjects/test/itkSpatialObjectTreeContainerIteratorTest.
cxx:36:   instantiated from here
Modules/Core/Common/include/itkPostOrderTreeIterator.h:169: error: invalid
conversion from 'itk::TreeNode<itk::SpatialObject<3u>*>*' to
'itk::SpatialObjectTreeNode<3u>*'
Modules/Core/Common/include/itkPostOrderTreeIterator.h: In member function
'const typename itk::PostOrderTreeIterator<TTreeType>::TreeNodeType*
itk::PostOrderTreeIterator<TTreeType>::FindNextNode() const [with
TTreeType = itk::SpatialObjectTreeContainer<3u>]':
Modules/Core/Common/include/itkPostOrderTreeIterator.h:94:   instantiated
from 'bool itk::PostOrderTreeIterator<TTreeType>::HasNext() const [with
TTreeType = itk::SpatialObjectTreeContainer<3u>]'
Modules/Core/SpatialObjects/test/itkSpatialObjectTreeContainerIteratorTest.
cxx:37:   instantiated from here
Modules/Core/Common/include/itkPostOrderTreeIterator.h:126: error: invalid
conversion from 'itk::TreeNode<itk::SpatialObject<3u>*>*' to 'const
itk::SpatialObjectTreeNode<3u>*'
Modules/Core/Common/include/itkPostOrderTreeIterator.h: In member function
'const typename itk::PostOrderTreeIterator<TTreeType>::TreeNodeType*
itk::PostOrderTreeIterator<TTreeType>::FindSister(typename
itk::TreeIteratorBase<TTreeType>::TreeNodeType*) const [with TTreeType =
itk::SpatialObjectTreeContainer<3u>]':
Modules/Core/Common/include/itkPostOrderTreeIterator.h:119:   instantiated
from 'const typename itk::PostOrderTreeIterator<TTreeType>::TreeNodeType*
itk::PostOrderTreeIterator<TTreeType>::FindNextNode() const [with
TTreeType = itk::SpatialObjectTreeContainer<3u>]'
Modules/Core/Common/include/itkPostOrderTreeIterator.h:94:   instantiated
from 'bool itk::PostOrderTreeIterator<TTreeType>::HasNext() const [with
TTreeType = itk::SpatialObjectTreeContainer<3u>]'
Modules/Core/SpatialObjects/test/itkSpatialObjectTreeContainerIteratorTest.
cxx:37:   instantiated from here
Modules/Core/Common/include/itkPostOrderTreeIterator.h:139: error: invalid
conversion from 'itk::TreeNode<itk::SpatialObject<3u>*>*' to
'itk::SpatialObjectTreeNode<3u>*'
Modules/Core/Common/include/itkPostOrderTreeIterator.h:145: error: invalid
conversion from 'itk::TreeNode<itk::SpatialObject<3u>*>*' to
'itk::SpatialObjectTreeNode<3u>*'



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