ENH: Add GradientImageFilter::OverrideBoundaryCondition(std::unique_ptr)

Added `GradientImageFilter::OverrideBoundaryCondition` overload, to allows
specifying the argument by a `unique_ptr`. Aims to make it more clear that the
filter takes the ownership of the specified `BoundaryCondition` object.

Triggered by a comment from Bradley Lowekamp at
#4512 (comment)
on March 13, 2024.

Modules/Filtering/ImageGradient/include/itkGradientImageFilter.h

@@ -145,6 +145,10 @@ class ITK_TEMPLATE_EXPORT GradientImageFilter : public ImageToImageFilter<TInput
   void
   OverrideBoundaryCondition(BoundaryConditionType * boundaryCondition);
 
+  /** Allows to change the default boundary condition */
+  void
+  OverrideBoundaryCondition(std::unique_ptr<BoundaryConditionType> boundaryCondition);
+
 #ifdef ITK_USE_CONCEPT_CHECKING
   // Begin concept checking
   itkConceptMacro(InputConvertibleToOutputCheck, (Concept::Convertible<InputPixelType, OutputValueType>));

Modules/Filtering/ImageGradient/include/itkGradientImageFilter.hxx

@@ -45,6 +45,14 @@ GradientImageFilter<TInputImage, TOperatorValueType, TOutputValue, TOutputImage>
   m_BoundaryCondition.reset(boundaryCondition);
 }
 
+template <typename TInputImage, typename TOperatorValueType, typename TOutputValue, typename TOutputImage>
+void
+GradientImageFilter<TInputImage, TOperatorValueType, TOutputValue, TOutputImage>::OverrideBoundaryCondition(
+  std::unique_ptr<BoundaryConditionType> boundaryCondition)
+{
+  m_BoundaryCondition = std::move(boundaryCondition);
+}
+
 template <typename TInputImage, typename TOperatorValueType, typename TOutputValueType, typename TOutputImageType>
 void
 GradientImageFilter<TInputImage, TOperatorValueType, TOutputValueType, TOutputImageType>::GenerateInputRequestedRegion()

Modules/Filtering/ImageGradient/test/itkGradientImageFilterTest.cxx

@@ -89,7 +89,7 @@ itkGradientImageFilterTest(int argc, char * argv[])
 
   using PeriodicBoundaryType = itk::PeriodicBoundaryCondition<InputImageType2>;
   // Test the OverrideBoundaryCondition setting;
-  filter2->OverrideBoundaryCondition(new PeriodicBoundaryType);
+  filter2->OverrideBoundaryCondition(std::make_unique<PeriodicBoundaryType>());
 
   ITK_EXERCISE_BASIC_OBJECT_METHODS(filter2, GradientImageFilter, ImageToImageFilter);