STYLE: Prefer = default to explicitly trivial implementations

This check replaces default bodies of special member functions with
= default;. The explicitly defaulted function declarations enable more
opportunities in optimization, because the compiler might treat
explicitly defaulted functions as trivial.

Additionally, the C++11 use of = default more clearly expreses the
intent for the special member functions.

Author: hjmjohnson

Modules/Bridge/VTK/src/itkVTKImageExportBase.cxx

@@ -23,7 +23,7 @@ namespace itk
  * Constructor sets up information for the image-type indepenedent
  * callbacks implemented in this superclass.
  */
-VTKImageExportBase::VTKImageExportBase() {}
+VTKImageExportBase::VTKImageExportBase() = default;
 
 void
 VTKImageExportBase::PrintSelf(std::ostream & os, Indent indent) const

Modules/Core/Common/include/itkConditionalConstIterator.h

@@ -72,13 +72,7 @@ class ITK_TEMPLATE_EXPORT ConditionalConstIterator
   /** operator= is provided to make sure the handle to the image is properly
    * reference counted. */
   Self &
-  operator=(const Self & it)
-  {
-    m_IsAtEnd = it.m_IsAtEnd; // copy the end flag
-    m_Image = it.m_Image;     // copy the smart pointer
-    m_Region = it.m_Region;   // copy the region
-    return *this;
-  }
+  operator=(const Self & it) = default;
 
   /** Get the dimension (size) of the index. */
   static unsigned int

Modules/Core/Common/include/itkConstShapedNeighborhoodIterator.h

@@ -127,12 +127,7 @@ class ITK_TEMPLATE_EXPORT ConstShapedNeighborhoodIterator : private Neighborhood
     ~ConstIterator() = default;
 
     ConstIterator &
-    operator=(const ConstIterator & o)
-    {
-      m_NeighborhoodIterator = o.m_NeighborhoodIterator;
-      m_ListIterator = o.m_ListIterator;
-      return *this;
-    }
+    operator=(const ConstIterator & o) = default;
 
     ConstIterator(const ConstIterator & o)
       : m_NeighborhoodIterator(o.m_NeighborhoodIterator)

Modules/Core/Common/include/itkDataObjectConstIterator.h

@@ -34,11 +34,7 @@ class DataObjectConstIterator
 
   DataObjectConstIterator() = default;
 
-  DataObjectConstIterator(const DataObjectConstIterator & iter)
-    : m_Iterator(iter.m_Iterator)
-    , m_Begin(iter.m_Begin)
-    , m_End(iter.m_End)
-  {}
+  DataObjectConstIterator(const DataObjectConstIterator & iter) = default;
 
   DataObjectConstIterator &
   operator=(const DataObjectConstIterator & iter)

Modules/Core/Common/include/itkDataObjectIterator.h

@@ -34,11 +34,7 @@ class DataObjectIterator
 
   DataObjectIterator() = default;
 
-  DataObjectIterator(const DataObjectIterator & iter)
-    : m_Iterator(iter.m_Iterator)
-    , m_Begin(iter.m_Begin)
-    , m_End(iter.m_End)
-  {}
+  DataObjectIterator(const DataObjectIterator & iter) = default;
 
   DataObjectIterator &
   operator=(const DataObjectIterator & iter)

Modules/Core/Common/include/itkImageRandomNonRepeatingConstIteratorWithIndex.h

@@ -44,7 +44,7 @@ class NodeOfPermutation
   SizeValueType m_Index{ 0 };
   double        m_Value{ 0.0 };
 
-  NodeOfPermutation() {}
+  NodeOfPermutation() = default;
 
   bool
   operator<(const NodeOfPermutation & b) const

Modules/Core/Common/include/itkVariableSizeMatrix.h

@@ -203,11 +203,7 @@ class ITK_TEMPLATE_EXPORT VariableSizeMatrix
 
   /** Assignment operator. */
   inline Self &
-  operator=(const Self & matrix)
-  {
-    m_Matrix = matrix.m_Matrix;
-    return *this;
-  }
+  operator=(const Self & matrix) = default;
 
   /** Return the inverse matrix. */
   inline vnl_matrix<T>

Modules/Core/Common/src/itkDataObject.cxx

@@ -43,10 +43,7 @@ DataObjectError::DataObjectError(std::string file, unsigned int lineNumber)
   : ExceptionObject(std::move(file), lineNumber)
 {}
 
-DataObjectError::DataObjectError(const DataObjectError & orig) noexcept
-  : ExceptionObject(orig)
-  , m_DataObject(orig.m_DataObject)
-{}
+DataObjectError::DataObjectError(const DataObjectError & orig) noexcept = default;
 
 DataObjectError &
 DataObjectError::operator=(const DataObjectError &) noexcept = default;

Modules/Core/Common/src/itkImageRegionSplitterDirection.cxx

@@ -22,7 +22,7 @@
 namespace itk
 {
 
-ImageRegionSplitterDirection::ImageRegionSplitterDirection() {}
+ImageRegionSplitterDirection::ImageRegionSplitterDirection() = default;
 
 void
 ImageRegionSplitterDirection::PrintSelf(std::ostream & os, Indent indent) const

Modules/Core/Common/src/itkLightProcessObject.cxx

@@ -22,7 +22,7 @@ namespace itk
 /**
  * Instantiate object with no start, end, or progress methods.
  */
-LightProcessObject::LightProcessObject() {}
+LightProcessObject::LightProcessObject() = default;
 
 /**
  * Destructor for the LightProcessObject class. We've got to