ENH: Replace PrintSelf NumericTraits-cast boilerplate with itk::print_helper::PrintNumericTrait helper (supersedes #3909)

Modules/Core/Common/include/itkAnnulusOperator.h

@@ -20,6 +20,7 @@
 
 #include "itkNeighborhoodOperator.h"
 #include "itkVector.h"
+#include "itkPrintHelper.h"
 
 namespace itk
 {
@@ -225,13 +226,10 @@ class ITK_TEMPLATE_EXPORT AnnulusOperator : public NeighborhoodOperator<TPixel,
     os << indent << "Thickness: " << m_Thickness << std::endl;
     os << indent << "Normalize: " << m_Normalize << std::endl;
     os << indent << "BrightCenter: " << m_BrightCenter << std::endl;
-    os << indent << "InteriorValue: " << static_cast<typename NumericTraits<PixelType>::PrintType>(m_InteriorValue)
-       << std::endl;
-    os << indent << "AnnulusValue: " << static_cast<typename NumericTraits<PixelType>::PrintType>(m_AnnulusValue)
-       << std::endl;
-    os << indent << "ExteriorValue: " << static_cast<typename NumericTraits<PixelType>::PrintType>(m_ExteriorValue)
-       << std::endl;
-    os << indent << "Spacing: " << static_cast<typename NumericTraits<SpacingType>::PrintType>(m_Spacing) << std::endl;
+    print_helper::PrintNumericTrait(os, indent, "InteriorValue", m_InteriorValue);
+    print_helper::PrintNumericTrait(os, indent, "AnnulusValue", m_AnnulusValue);
+    print_helper::PrintNumericTrait(os, indent, "ExteriorValue", m_ExteriorValue);
+    print_helper::PrintNumericTrait(os, indent, "Spacing", m_Spacing);
   }
 
 protected:

Modules/Core/Common/include/itkBinaryThresholdSpatialFunction.hxx

@@ -19,6 +19,7 @@
 #define itkBinaryThresholdSpatialFunction_hxx
 
 
+#include "itkPrintHelper.h"
 namespace itk
 {
 
@@ -28,12 +29,8 @@ BinaryThresholdSpatialFunction<TFunction>::PrintSelf(std::ostream & os, Indent i
 {
   Superclass::PrintSelf(os, indent);
 
-  os << indent
-     << "LowerThreshold: " << static_cast<typename NumericTraits<FunctionOutputType>::PrintType>(m_LowerThreshold)
-     << std::endl;
-  os << indent
-     << "UpperThreshold: " << static_cast<typename NumericTraits<FunctionOutputType>::PrintType>(m_UpperThreshold)
-     << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "LowerThreshold", m_LowerThreshold);
+  print_helper::PrintNumericTrait(os, indent, "UpperThreshold", m_UpperThreshold);
 
   itkPrintSelfObjectMacro(Function);
 }

Modules/Core/Common/include/itkImageDuplicator.hxx

@@ -19,6 +19,7 @@
 #define itkImageDuplicator_hxx
 
 #include "itkImageAlgorithm.h"
+#include "itkPrintHelper.h"
 
 namespace itk
 {
@@ -64,8 +65,7 @@ ImageDuplicator<TInputImage>::PrintSelf(std::ostream & os, Indent indent) const
   itkPrintSelfObjectMacro(InputImage);
   itkPrintSelfObjectMacro(DuplicateImage);
 
-  os << indent << "InternalImageTime: " << static_cast<NumericTraits<ModifiedTimeType>::PrintType>(m_InternalImageTime)
-     << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "InternalImageTime", m_InternalImageTime);
 }
 } // end namespace itk
 

Modules/Core/Common/include/itkMinimumMaximumImageCalculator.hxx

@@ -19,6 +19,7 @@
 #define itkMinimumMaximumImageCalculator_hxx
 
 #include "itkImageRegionConstIteratorWithIndex.h"
+#include "itkPrintHelper.h"
 
 namespace itk
 {
@@ -113,8 +114,8 @@ MinimumMaximumImageCalculator<TInputImage>::PrintSelf(std::ostream & os, Indent
 {
   Superclass::PrintSelf(os, indent);
 
-  os << indent << "Minimum: " << static_cast<typename NumericTraits<PixelType>::PrintType>(m_Minimum) << std::endl;
-  os << indent << "Maximum: " << static_cast<typename NumericTraits<PixelType>::PrintType>(m_Maximum) << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "Minimum", m_Minimum);
+  print_helper::PrintNumericTrait(os, indent, "Maximum", m_Maximum);
   os << indent << "Index of Minimum: " << m_IndexOfMinimum << std::endl;
   os << indent << "Index of Maximum: " << m_IndexOfMaximum << std::endl;
   itkPrintSelfObjectMacro(Image);

Modules/Core/Common/include/itkNeighborhood.hxx

@@ -117,8 +117,8 @@ void
 Neighborhood<TPixel, VDimension, TContainer>::PrintSelf(std::ostream & os, Indent indent) const
 {
   using namespace itk::print_helper;
-  os << indent << "Size: " << static_cast<typename NumericTraits<SizeType>::PrintType>(m_Size) << std::endl;
-  os << indent << "Radius: " << static_cast<typename NumericTraits<SizeType>::PrintType>(m_Radius) << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "Size", m_Size);
+  print_helper::PrintNumericTrait(os, indent, "Radius", m_Radius);
   os << indent << "StrideTable: " << m_StrideTable << std::endl;
   os << indent << "OffsetTable: " << m_OffsetTable << std::endl;
 }

Modules/Core/Common/include/itkObjectStore.hxx

@@ -134,9 +134,8 @@ ObjectStore<TObjectType>::PrintSelf(std::ostream & os, Indent indent) const
   Superclass::PrintSelf(os, indent);
 
   os << indent << "GrowthStrategy: " << m_GrowthStrategy << std::endl;
-  os << indent << "Size: " << static_cast<NumericTraits<SizeValueType>::PrintType>(m_Size) << std::endl;
-  os << indent << "LinearGrowthSize: " << static_cast<NumericTraits<SizeValueType>::PrintType>(m_LinearGrowthSize)
-     << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "Size", m_Size);
+  print_helper::PrintNumericTrait(os, indent, "LinearGrowthSize", m_LinearGrowthSize);
   os << indent << "FreeList: " << m_FreeList << std::endl;
 }
 } // end namespace itk

Modules/Core/Common/include/itkPointSetToImageFilter.hxx

@@ -22,6 +22,7 @@
 #include "itkBoundingBox.h"
 #include "itkNumericTraits.h"
 #include "itkMath.h"
+#include "itkPrintHelper.h"
 
 namespace itk
 {
@@ -227,10 +228,8 @@ PointSetToImageFilter<TInputPointSet, TOutputImage>::PrintSelf(std::ostream & os
   os << indent << "Origin: " << m_Origin << std::endl;
   os << indent << "Spacing: " << m_Spacing << std::endl;
   os << indent << "Direction: " << m_Direction << std::endl;
-  os << indent << "Inside Value : " << static_cast<typename NumericTraits<ValueType>::PrintType>(m_InsideValue)
-     << std::endl;
-  os << indent << "Outside Value : " << static_cast<typename NumericTraits<ValueType>::PrintType>(m_OutsideValue)
-     << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "Inside Value ", m_InsideValue);
+  print_helper::PrintNumericTrait(os, indent, "Outside Value ", m_OutsideValue);
 }
 } // end namespace itk
 

Modules/Core/Common/include/itkPrintHelper.h

@@ -19,6 +19,8 @@
 #ifndef itkPrintHelper_h
 #define itkPrintHelper_h
 
+#include "itkIndent.h"
+
 #include <array>
 #include <iostream>
 #include <iterator>
@@ -27,13 +29,27 @@
 #include <type_traits>
 
 
+namespace itk
+{
+// Forward declaration so itkPrintHelper.h can be safely included from
+// itkMacro.h without re-entering itkNumericTraits.h (which itself uses
+// macros defined later in itkMacro.h).  Every PrintNumericTrait() call
+// site needs the full NumericTraits<T> specialization in scope, but those
+// sites already #include "itkNumericTraits.h" directly or transitively.
+template <typename T>
+class NumericTraits;
+} // namespace itk
+
 namespace itk::print_helper
 {
 
 // Forward declarations so the per-container bodies below see all overloads at
 // definition time.  Required for nested cases like vector<list<T>>, where the
 // recursive `os << *it` is parsed before the list overload would otherwise be
 // declared, and ADL on std container types never reaches itk::print_helper.
+// PrintNumericTrait further down also dispatches through `os << value` and
+// must see these forward declarations to instantiate against std container
+// member types at the call site.
 template <typename T>
 std::ostream &
 operator<<(std::ostream & os, const std::vector<T> & v);
@@ -50,6 +66,48 @@ template <typename T, size_t VLength, typename = std::enable_if_t<!std::is_same_
 std::ostream &
 operator<<(std::ostream & os, const T (&arr)[VLength]);
 
+/** \brief Print "<name>: <value>\n" indented, matching ITK's PrintSelf style.
+ *
+ * Formats and writes a single named member to \a os preceded by \a indent,
+ * followed by a newline.  When \c NumericTraits<T>::PrintType differs from
+ * \a T (the relevant case being the \c char family, whose \c PrintType is
+ * \c int, so values render numerically rather than as ASCII characters) the
+ * value is forwarded through a \c static_cast.  When the two types coincide
+ * (the common case, including all built-in scalars wider than \c char and
+ * \c std::complex specialisations whose \c PrintType is \c Self) the cast
+ * step is skipped entirely so the value's own stream insertion overload is
+ * selected directly.
+ *
+ * Equivalent to the boilerplate
+ * \code
+ *   os << indent << "Name: "
+ *      << static_cast<typename NumericTraits<T>::PrintType>(m_Name)
+ *      << std::endl;
+ * \endcode
+ * but with explicit \a os and \a indent parameters and no preprocessor
+ * macro expansion.
+ *
+ * Typical use inside a \c PrintSelf override:
+ * \code
+ *   print_helper::PrintNumericTrait(os, indent, "Threshold", m_Threshold);
+ * \endcode
+ */
+template <typename T>
+inline void
+PrintNumericTrait(std::ostream & os, const Indent & indent, const char * name, const T & value)
+{
+  os << indent << name << ": ";
+  if constexpr (std::is_same_v<T, typename NumericTraits<T>::PrintType>)
+  {
+    os << value;
+  }
+  else
+  {
+    os << static_cast<typename NumericTraits<T>::PrintType>(value);
+  }
+  os << std::endl;
+}
+
 template <typename T>
 std::ostream &
 operator<<(std::ostream & os, const std::vector<T> & v)

Modules/Core/Common/include/itkResourceProbe.hxx

@@ -58,24 +58,16 @@ ResourceProbe<ValueType, MeanType>::Print(std::ostream & os, Indent indent) cons
 {
   using namespace print_helper;
 
-  os << indent << "StartValue: " << static_cast<typename NumericTraits<ValueType>::PrintType>(m_StartValue)
-     << std::endl;
-  os << indent << "TotalValue: " << static_cast<typename NumericTraits<ValueType>::PrintType>(m_TotalValue)
-     << std::endl;
-  os << indent << "MinimumValue: " << static_cast<typename NumericTraits<ValueType>::PrintType>(m_MinimumValue)
-     << std::endl;
-  os << indent << "MaximumValue: " << static_cast<typename NumericTraits<ValueType>::PrintType>(m_MaximumValue)
-     << std::endl;
-  os << indent
-     << "StandardDeviation: " << static_cast<typename NumericTraits<ValueType>::PrintType>(m_StandardDeviation)
-     << std::endl;
-  os << indent << "StandardError: " << static_cast<typename NumericTraits<ValueType>::PrintType>(m_StandardError)
-     << std::endl;
-
-  os << indent << "NumberOfStarts: " << static_cast<NumericTraits<CountType>::PrintType>(m_NumberOfStarts) << std::endl;
-  os << indent << "NumberOfStops: " << static_cast<NumericTraits<CountType>::PrintType>(m_NumberOfStops) << std::endl;
-  os << indent << "NumberOfIteration: " << static_cast<NumericTraits<CountType>::PrintType>(m_NumberOfIteration)
-     << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "StartValue", m_StartValue);
+  print_helper::PrintNumericTrait(os, indent, "TotalValue", m_TotalValue);
+  print_helper::PrintNumericTrait(os, indent, "MinimumValue", m_MinimumValue);
+  print_helper::PrintNumericTrait(os, indent, "MaximumValue", m_MaximumValue);
+  print_helper::PrintNumericTrait(os, indent, "StandardDeviation", m_StandardDeviation);
+  print_helper::PrintNumericTrait(os, indent, "StandardError", m_StandardError);
+
+  print_helper::PrintNumericTrait(os, indent, "NumberOfStarts", m_NumberOfStarts);
+  print_helper::PrintNumericTrait(os, indent, "NumberOfStops", m_NumberOfStops);
+  print_helper::PrintNumericTrait(os, indent, "NumberOfIteration", m_NumberOfIteration);
 
   os << indent << "ProbeValueList: " << m_ProbeValueList << std::endl;
 

Modules/Core/Common/test/itkPrintHelperGTest.cxx

@@ -20,6 +20,7 @@
 #include "itkOffset.h"
 #include "gtest/gtest.h"
 #include <array>
+#include <complex>
 #include <sstream>
 #include <vector>
 #include <list>
@@ -130,3 +131,55 @@ TEST(PrintHelper, ArrayOfVector)
   oss << a;
   EXPECT_EQ(oss.str(), "([1, 2], [3])");
 }
+
+TEST(PrintHelper, PrintNumericTraitDouble)
+{
+  std::ostringstream oss;
+  itk::print_helper::PrintNumericTrait(oss, itk::Indent{}, "Value", 3.5);
+  EXPECT_EQ(oss.str(), "Value: 3.5\n");
+}
+
+TEST(PrintHelper, PrintNumericTraitIntIsIdentityCast)
+{
+  // PrintType<int> == int, so the constexpr branch skips static_cast and
+  // streams the value directly.
+  std::ostringstream oss;
+  itk::print_helper::PrintNumericTrait(oss, itk::Indent{}, "Count", 42);
+  EXPECT_EQ(oss.str(), "Count: 42\n");
+}
+
+TEST(PrintHelper, PrintNumericTraitCharRendersNumerically)
+{
+  // PrintType<unsigned char> == int.  Without the cast the value would be
+  // emitted as the ASCII character; the helper must produce the integer.
+  std::ostringstream  oss;
+  const unsigned char ch = 65;
+  itk::print_helper::PrintNumericTrait(oss, itk::Indent{}, "Byte", ch);
+  EXPECT_EQ(oss.str(), "Byte: 65\n");
+}
+
+TEST(PrintHelper, PrintNumericTraitSignedCharRendersNumerically)
+{
+  std::ostringstream oss;
+  const signed char  sc = -7;
+  itk::print_helper::PrintNumericTrait(oss, itk::Indent{}, "Offset", sc);
+  EXPECT_EQ(oss.str(), "Offset: -7\n");
+}
+
+TEST(PrintHelper, PrintNumericTraitComplexIsIdentityCast)
+{
+  // NumericTraits<std::complex<T>>::PrintType is Self, so PrintNumericTrait
+  // forwards to the value's own ostream insertion overload unchanged.
+  std::ostringstream   oss;
+  std::complex<double> z{ 1.0, -2.5 };
+  itk::print_helper::PrintNumericTrait(oss, itk::Indent{}, "Z", z);
+  EXPECT_EQ(oss.str(), "Z: (1,-2.5)\n");
+}
+
+TEST(PrintHelper, PrintNumericTraitIndentation)
+{
+  std::ostringstream oss;
+  itk::Indent        indent{ 4 };
+  itk::print_helper::PrintNumericTrait(oss, indent, "Threshold", 0.125);
+  EXPECT_EQ(oss.str(), "    Threshold: 0.125\n");
+}

Modules/Core/GPUCommon/include/itkGPUReduction.hxx

@@ -19,6 +19,7 @@
 #define itkGPUReduction_hxx
 
 #include "itkMacro.h"
+#include "itkPrintHelper.h"
 
 // #define CPU_VERIFY
 
@@ -59,8 +60,8 @@ GPUReduction<TElement>::PrintSelf(std::ostream & os, Indent indent) const
   os << indent << "Size: " << m_Size << std::endl;
   itkPrintSelfBooleanMacro(SmallBlock);
 
-  os << indent << "GPUResult: " << static_cast<typename NumericTraits<TElement>::PrintType>(m_GPUResult) << std::endl;
-  os << indent << "CPUResult: " << static_cast<typename NumericTraits<TElement>::PrintType>(m_CPUResult) << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "GPUResult", m_GPUResult);
+  print_helper::PrintNumericTrait(os, indent, "CPUResult", m_CPUResult);
 }
 
 template <typename TElement>

Modules/Core/ImageFunction/include/itkBSplineInterpolateImageFunction.hxx

@@ -59,9 +59,7 @@ BSplineInterpolateImageFunction<TImageType, TCoordinate, TCoefficientType>::Prin
   Superclass::PrintSelf(os, indent);
 
   os << indent << "Scratch: " << m_Scratch << std::endl;
-  os << indent
-     << "DataLength: " << static_cast<typename NumericTraits<typename TImageType::SizeType>::PrintType>(m_DataLength)
-     << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "DataLength", m_DataLength);
   os << indent << "SplineOrder: " << m_SplineOrder << std::endl;
 
   itkPrintSelfObjectMacro(Coefficients);
@@ -73,8 +71,7 @@ BSplineInterpolateImageFunction<TImageType, TCoordinate, TCoefficientType>::Prin
 
   itkPrintSelfBooleanMacro(UseImageDirection);
 
-  os << indent << "NumberOfWorkUnits: " << static_cast<NumericTraits<ThreadIdType>::PrintType>(m_NumberOfWorkUnits)
-     << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "NumberOfWorkUnits", m_NumberOfWorkUnits);
 
   os << indent << "ThreadedEvaluateIndex: ";
   if (m_ThreadedEvaluateIndex != nullptr)

Modules/Core/ImageFunction/include/itkNeighborhoodOperatorImageFunction.hxx

@@ -22,6 +22,7 @@
 #include "itkConstNeighborhoodIterator.h"
 
 #include <cassert>
+#include "itkPrintHelper.h"
 
 namespace itk
 {
@@ -32,8 +33,7 @@ NeighborhoodOperatorImageFunction<TInputImage, TOutput>::PrintSelf(std::ostream
 {
   Superclass::PrintSelf(os, indent);
 
-  os << indent << "Operator: " << static_cast<typename NumericTraits<NeighborhoodType>::PrintType>(m_Operator)
-     << std::endl;
+  print_helper::PrintNumericTrait(os, indent, "Operator", m_Operator);
 }
 
 template <typename TInputImage, typename TOutput>