STYLE: Add in-class {} initializers to classes with virtual functions

Added in-class `{}` default member initializers to data members of classes
that have one or more virtual member functions.

For an object that has one or more virtual member functions, the performance
cost of adding a `{}` default member initializer to each of its non-static data
members should be acceptable, relative to cost of the initialization of its
virtual table.

Follow-up to pull request InsightSoftwareConsortium#3851
commit 5e2c49f
"STYLE: Add in-class `{}` member initializers to objects created by New()"
(which only looked at classes that have a `itkNewMacro`).

Modules/Bridge/VTK/include/itkVTKImageExportBase.h

@@ -231,7 +231,7 @@ class ITKVTK_EXPORT VTKImageExportBase : public ProcessObject
 
 private:
   /** PipelineMTime from the last call to PipelineModifiedCallback. */
-  ModifiedTimeType m_LastPipelineMTime;
+  ModifiedTimeType m_LastPipelineMTime{};
 };
 } // end namespace itk
 

Modules/Compatibility/Deprecated/include/itkChildTreeIterator.h

@@ -81,8 +81,8 @@ class ITK_TEMPLATE_EXPORT ChildTreeIterator : public TreeIteratorBase<TTreeType>
   HasNext() const override;
 
 private:
-  mutable ChildIdentifier m_ListPosition;
-  TreeNodeType *          m_ParentNode;
+  mutable ChildIdentifier m_ListPosition{};
+  TreeNodeType *          m_ParentNode{};
 };
 
 } // end namespace itk

Modules/Compatibility/Deprecated/include/itkLevelOrderTreeIterator.h

@@ -106,9 +106,9 @@ class ITK_TEMPLATE_EXPORT LevelOrderTreeIterator : public TreeIteratorBase<TTree
   int
   GetLevel(const TreeNodeType * node) const;
 
-  int                                      m_StartLevel;
-  int                                      m_EndLevel;
-  mutable std::queue<const TreeNodeType *> m_Queue;
+  int                                      m_StartLevel{};
+  int                                      m_EndLevel{};
+  mutable std::queue<const TreeNodeType *> m_Queue{};
 };
 
 } // end namespace itk

Modules/Compatibility/Deprecated/include/itkMutexLock.h

@@ -102,7 +102,7 @@ class ITKDeprecated_EXPORT SimpleMutexLock
   }
 
 protected:
-  MutexType m_MutexLock;
+  MutexType m_MutexLock{};
 };
 
 /**

Modules/Compatibility/Deprecated/include/itkTreeChangeEvent.h

@@ -85,7 +85,7 @@ class ITK_TEMPLATE_EXPORT TreeChangeEvent : public ModifiedEvent
   {}
 
 protected:
-  const TreeIteratorBase<TTreeType> * m_ChangePosition;
+  const TreeIteratorBase<TTreeType> * m_ChangePosition{};
 };
 
 /**  \class TreeNodeChangeEvent

Modules/Compatibility/Deprecated/include/itkTreeIteratorBase.h

@@ -274,9 +274,9 @@ class ITK_TEMPLATE_EXPORT TreeIteratorBase
   TreeIteratorBase(const TTreeType * tree, const TreeNodeType * start);
 
   mutable TreeNodeType * m_Position; // Current position of the iterator
-  mutable TreeNodeType * m_Begin;
-  const TreeNodeType *   m_Root;
-  TTreeType *            m_Tree;
+  mutable TreeNodeType * m_Begin{};
+  const TreeNodeType *   m_Root{};
+  TTreeType *            m_Tree{};
 
   virtual bool
   HasNext() const = 0;

Modules/Core/Common/include/itkCellInterface.h

@@ -490,7 +490,7 @@ class ITK_TEMPLATE_EXPORT CellInterface
 
 protected:
   /** Store the set of cells using this boundary. */
-  UsingCellsContainer m_UsingCells;
+  UsingCellsContainer m_UsingCells{};
 };
 
 /** \class CellTraitsInfo

Modules/Core/Common/include/itkConditionalConstIterator.h

@@ -112,10 +112,10 @@ class ITK_TEMPLATE_EXPORT ConditionalConstIterator
 protected: // made protected so other iterators can access
   /** Smart pointer to the source image. */
   // SmartPointer<const ImageType> m_Image;
-  typename ImageType::ConstWeakPointer m_Image;
+  typename ImageType::ConstWeakPointer m_Image{};
 
   /** Region type to iterate over. */
-  RegionType m_Region;
+  RegionType m_Region{};
 
   /** Is the iterator at the end of its walk? */
   bool m_IsAtEnd{ false };

Modules/Core/Common/include/itkConstNeighborhoodIterator.h

@@ -590,7 +590,7 @@ class ITK_TEMPLATE_EXPORT ConstNeighborhoodIterator
   const InternalPixelType * m_Begin{ nullptr };
 
   /** The image on which iteration is defined. */
-  typename ImageType::ConstWeakPointer m_ConstImage;
+  typename ImageType::ConstWeakPointer m_ConstImage{};
 
   /** A pointer to one past the last pixel in the iteration region. */
   const InternalPixelType * m_End{ nullptr };
@@ -603,7 +603,7 @@ class ITK_TEMPLATE_EXPORT ConstNeighborhoodIterator
   IndexType m_Loop{ { 0 } };
 
   /** The region over which iteration is defined. */
-  RegionType m_Region;
+  RegionType m_Region{};
 
   /** The internal array of offsets that provide support for regions of
    *  interest.
@@ -616,7 +616,7 @@ class ITK_TEMPLATE_EXPORT ConstNeighborhoodIterator
    * By default this points to m_BoundaryCondition, but
    * OverrideBoundaryCondition allows a user to point this variable an external
    * boundary condition.  */
-  ImageBoundaryConditionPointerType m_BoundaryCondition;
+  ImageBoundaryConditionPointerType m_BoundaryCondition{};
 
   /** Denotes which of the iterators dimensional sides spill outside
    * region of interest boundaries. By default `false` for each dimension. */
@@ -631,19 +631,19 @@ class ITK_TEMPLATE_EXPORT ConstNeighborhoodIterator
   mutable bool m_IsInBoundsValid{ false };
 
   /** Lower threshold of in-bounds loop counter values. */
-  IndexType m_InnerBoundsLow;
+  IndexType m_InnerBoundsLow{};
 
   /** Upper threshold of in-bounds loop counter values. */
-  IndexType m_InnerBoundsHigh;
+  IndexType m_InnerBoundsHigh{};
 
   /** Default boundary condition. */
-  TBoundaryCondition m_InternalBoundaryCondition;
+  TBoundaryCondition m_InternalBoundaryCondition{};
 
   /** Does the specified region need to worry about boundary conditions? */
   bool m_NeedToUseBoundaryCondition{ false };
 
   /** Functor type used to access neighborhoods of pixel pointers */
-  NeighborhoodAccessorFunctorType m_NeighborhoodAccessorFunctor;
+  NeighborhoodAccessorFunctorType m_NeighborhoodAccessorFunctor{};
 };
 
 template <typename TImage>

Modules/Core/Common/include/itkConstNeighborhoodIteratorWithOnlyIndex.h

@@ -375,7 +375,7 @@ class ITK_TEMPLATE_EXPORT ConstNeighborhoodIteratorWithOnlyIndex : public Neighb
   IndexType m_Bound{ { 0 } };
 
   /** The image on which iteration is defined. */
-  typename ImageType::ConstPointer m_ConstImage;
+  typename ImageType::ConstPointer m_ConstImage{};
 
   /** The end index for iteration within the itk::Image region
    * on which this ConstNeighborhoodIteratorWithOnlyIndex is defined. */
@@ -385,7 +385,7 @@ class ITK_TEMPLATE_EXPORT ConstNeighborhoodIteratorWithOnlyIndex : public Neighb
   IndexType m_Loop{ { 0 } };
 
   /** The region over which iteration is defined. */
-  RegionType m_Region;
+  RegionType m_Region{};
 
   /** Denotes which of the iterators dimensional sides spill outside
    * region of interest boundaries. By default `false` for each dimension. */
@@ -400,10 +400,10 @@ class ITK_TEMPLATE_EXPORT ConstNeighborhoodIteratorWithOnlyIndex : public Neighb
   mutable bool m_IsInBoundsValid{ false };
 
   /** Lower threshold of in-bounds loop counter values. */
-  IndexType m_InnerBoundsLow;
+  IndexType m_InnerBoundsLow{};
 
   /** Upper threshold of in-bounds loop counter values. */
-  IndexType m_InnerBoundsHigh;
+  IndexType m_InnerBoundsHigh{};
 
   /** Does the specified region need to worry about boundary conditions? */
   bool m_NeedToUseBoundaryCondition{ false };

Modules/Core/Common/include/itkConstShapedNeighborhoodIterator.h

@@ -421,7 +421,7 @@ class ITK_TEMPLATE_EXPORT ConstShapedNeighborhoodIterator : private Neighborhood
 
 
   bool          m_CenterIsActive{ false };
-  IndexListType m_ActiveIndexList;
+  IndexListType m_ActiveIndexList{};
 };
 } // namespace itk
 

Modules/Core/Common/include/itkConstantBoundaryCondition.h

@@ -157,7 +157,7 @@ class ITK_TEMPLATE_EXPORT ConstantBoundaryCondition : public ImageBoundaryCondit
   GetPixel(const IndexType & index, const TInputImage * image) const override;
 
 private:
-  OutputPixelType m_Constant;
+  OutputPixelType m_Constant{};
 };
 } // end namespace itk
 

Modules/Core/Common/include/itkCorrespondenceDataStructureIterator.h

@@ -95,19 +95,19 @@ class ITK_TEMPLATE_EXPORT CorrespondenceDataStructureIterator
     return m_CorrespondingListPointer;
   }
 
-  CorrespondingListIterator m_CorrespondingListIterator;
-  SecondaryNodeListIterator m_SecondaryListIterator;
+  CorrespondingListIterator m_CorrespondingListIterator{};
+  SecondaryNodeListIterator m_SecondaryListIterator{};
 
-  typename TStructureType::NodeListType::iterator m_NodeListIterator;
+  typename TStructureType::NodeListType::iterator m_NodeListIterator{};
 
 protected:
   /** Is the iterator at the end of its walk? */
-  bool                    m_IsAtEnd;
-  TStructureType *        m_Structure;
-  ItemType *              m_CorrespondingNodePointer;
-  CorrespondingListType * m_CorrespondingListPointer;
-  SecondaryNodeListType * m_SecondaryListPointer;
-  NodeListType *          m_NodeListPointer;
+  bool                    m_IsAtEnd{};
+  TStructureType *        m_Structure{};
+  ItemType *              m_CorrespondingNodePointer{};
+  CorrespondingListType * m_CorrespondingListPointer{};
+  SecondaryNodeListType * m_SecondaryListPointer{};
+  NodeListType *          m_NodeListPointer{};
 };
 } // end namespace itk
 

Modules/Core/Common/include/itkDomainThreader.h

@@ -163,7 +163,7 @@ class ITK_TEMPLATE_EXPORT DomainThreader : public Object
   static ITK_THREAD_RETURN_FUNCTION_CALL_CONVENTION
   ThreaderCallback(void * arg);
 
-  AssociateType * m_Associate;
+  AssociateType * m_Associate{};
 
 private:
   void
@@ -180,10 +180,10 @@ class ITK_TEMPLATE_EXPORT DomainThreader : public Object
    * well into that number.
    * This value is determined at the beginning of \c Execute(). */
   ThreadIdType                            m_NumberOfWorkUnitsUsed{ 0 };
-  ThreadIdType                            m_NumberOfWorkUnits;
-  typename DomainPartitionerType::Pointer m_DomainPartitioner;
-  DomainType                              m_CompleteDomain;
-  MultiThreaderBase::Pointer              m_MultiThreader;
+  ThreadIdType                            m_NumberOfWorkUnits{};
+  typename DomainPartitionerType::Pointer m_DomainPartitioner{};
+  DomainType                              m_CompleteDomain{};
+  MultiThreaderBase::Pointer              m_MultiThreader{};
 };
 
 } // namespace itk

Modules/Core/Common/include/itkExceptionObject.h

@@ -132,7 +132,7 @@ class ITKCommon_EXPORT ExceptionObject : public std::exception
 private:
   class ExceptionData;
 
-  std::shared_ptr<const ExceptionData> m_ExceptionData;
+  std::shared_ptr<const ExceptionData> m_ExceptionData{};
 };
 
 /** Generic inserter operator for ExceptionObject and its subclasses. */

Modules/Core/Common/include/itkFloodFilledFunctionConditionalConstIterator.h

@@ -239,40 +239,40 @@ class ITK_TEMPLATE_EXPORT FloodFilledFunctionConditionalConstIterator : public C
 
 protected: // made protected so other iterators can access
   /** Smart pointer to the function we're evaluating */
-  SmartPointer<FunctionType> m_Function;
+  SmartPointer<FunctionType> m_Function{};
 
   /** A temporary image used for storing info about indices
    * 0 = pixel has not yet been processed
    * 1 = pixel is not inside the function
    * 2 = pixel is inside the function, neighbor check incomplete
    * 3 = pixel is inside the function, neighbor check complete */
   using TTempImage = Image<unsigned char, Self::NDimensions>;
-  typename TTempImage::Pointer m_TemporaryPointer;
+  typename TTempImage::Pointer m_TemporaryPointer{};
 
   /** A list of locations to start the recursive fill */
-  SeedsContainerType m_Seeds;
+  SeedsContainerType m_Seeds{};
 
   /** The origin of the source image */
-  typename ImageType::PointType m_ImageOrigin;
+  typename ImageType::PointType m_ImageOrigin{};
 
   /** The spacing of the source image */
-  typename ImageType::SpacingType m_ImageSpacing;
+  typename ImageType::SpacingType m_ImageSpacing{};
 
   /** Region of the source image */
-  RegionType m_ImageRegion;
+  RegionType m_ImageRegion{};
 
   /** Stack used to hold the path of the iterator through the image */
-  std::queue<IndexType> m_IndexStack;
+  std::queue<IndexType> m_IndexStack{};
 
   /** Location vector used in the flood algorithm */
-  FunctionInputType m_LocationVector;
+  FunctionInputType m_LocationVector{};
 
   /** Indicates whether or not we've found a neighbor that needs to be
    * checked.  */
-  bool m_FoundUncheckedNeighbor;
+  bool m_FoundUncheckedNeighbor{};
 
   /** Indicates whether or not an index is valid (inside an image)/ */
-  bool m_IsValidIndex;
+  bool m_IsValidIndex{};
 };
 } // end namespace itk
 

Modules/Core/Common/include/itkFloodFilledSpatialFunctionConditionalConstIterator.h

@@ -125,7 +125,7 @@ class ITK_TEMPLATE_EXPORT FloodFilledSpatialFunctionConditionalConstIterator
    * 3) Intersect: if any of the corners of the pixel in physical space are inside the function,
    * then the pixel is inside the function */
 
-  unsigned char m_InclusionStrategy;
+  unsigned char m_InclusionStrategy{};
 };
 } // end namespace itk
 

Modules/Core/Common/include/itkImageConstIterator.h

@@ -377,18 +377,18 @@ class ITK_TEMPLATE_EXPORT ImageConstIterator
   }
 
 protected: // made protected so other iterators can access
-  typename TImage::ConstWeakPointer m_Image;
+  typename TImage::ConstWeakPointer m_Image{};
 
   RegionType m_Region; // region to iterate over
 
-  OffsetValueType m_Offset;
+  OffsetValueType m_Offset{};
   OffsetValueType m_BeginOffset; // offset to first pixel in region
   OffsetValueType m_EndOffset;   // offset to one pixel past last pixel in region
 
-  const InternalPixelType * m_Buffer;
+  const InternalPixelType * m_Buffer{};
 
-  AccessorType        m_PixelAccessor;
-  AccessorFunctorType m_PixelAccessorFunctor;
+  AccessorType        m_PixelAccessor{};
+  AccessorFunctorType m_PixelAccessorFunctor{};
 };
 } // end namespace itk
 

Modules/Core/Common/include/itkImageKernelOperator.h

@@ -87,7 +87,7 @@ class ITK_TEMPLATE_EXPORT ImageKernelOperator : public NeighborhoodOperator<TPix
   Fill(const CoefficientVector & coeff) override;
 
 private:
-  typename ImageType::ConstPointer m_ImageKernel;
+  typename ImageType::ConstPointer m_ImageKernel{};
 };
 } // namespace itk
 

Modules/Core/Common/include/itkImageReverseConstIterator.h

@@ -391,18 +391,18 @@ class ITK_TEMPLATE_EXPORT ImageReverseConstIterator
   }
 
 protected: // made protected so other iterators can access
-  typename ImageType::ConstWeakPointer m_Image;
+  typename ImageType::ConstWeakPointer m_Image{};
 
   RegionType m_Region; // region to iterate over
 
-  SizeValueType m_Offset;
+  SizeValueType m_Offset{};
   SizeValueType m_BeginOffset; // offset to last pixel in region
   SizeValueType m_EndOffset;   // offset to one pixel before first pixel
 
-  const InternalPixelType * m_Buffer;
+  const InternalPixelType * m_Buffer{};
 
-  AccessorType        m_PixelAccessor;
-  AccessorFunctorType m_PixelAccessorFunctor;
+  AccessorType        m_PixelAccessor{};
+  AccessorFunctorType m_PixelAccessorFunctor{};
 };
 } // end namespace itk
 

Modules/Core/Common/include/itkImageSink.h

@@ -189,8 +189,8 @@ class ImageSink
 
 private:
   unsigned int          m_NumberOfStreamDivisions{ 1 };
-  RegionSplitterPointer m_RegionSplitter;
-  InputImageRegionType  m_CurrentInputRegion;
+  RegionSplitterPointer m_RegionSplitter{};
+  InputImageRegionType  m_CurrentInputRegion{};
 
   /**
    *  Tolerances for checking whether input images are defined to

Modules/Core/Common/include/itkImageSource.h

@@ -399,7 +399,7 @@ class ITK_TEMPLATE_EXPORT ImageSource
   itkSetMacro(DynamicMultiThreading, bool);
   itkBooleanMacro(DynamicMultiThreading);
 
-  bool m_DynamicMultiThreading;
+  bool m_DynamicMultiThreading{};
 };
 } // end namespace itk
 

Modules/Core/Common/include/itkImageToImageFilter.h

@@ -378,8 +378,8 @@ class ITK_TEMPLATE_EXPORT ImageToImageFilter
    *  Tolerances for checking whether input images are defined to
    *  occupy the same physical space.
    */
-  double m_CoordinateTolerance;
-  double m_DirectionTolerance;
+  double m_CoordinateTolerance{};
+  double m_DirectionTolerance{};
 };
 } // end namespace itk