STYLE: Prefer constexpr for const numeric literals

Use constexpr for constant numeric literals.

Author: hjmjohnson

examples/example.cxx

@@ -20,7 +20,7 @@
 int example_gradientdescent( int argc, char* argv[] )
 {
 // Typedefs
-const unsigned int Dimension = 2;
+constexpr unsigned int Dimension = 2;
 using PixelType = float;
 using OutputPixelType = unsigned char;
 using ImageType = itk::Image< PixelType, Dimension >;
@@ -124,7 +124,7 @@ return EXIT_SUCCESS;
 int example_regularstepgradientdescent( int argc, char* argv[] )
 {
 // Typedefs
-const unsigned int Dimension = 2;
+constexpr unsigned int Dimension = 2;
 using PixelType = float;
 using OutputPixelType = unsigned char;
 using ImageType = itk::Image< PixelType, Dimension >;

include/itkSingleImageCostFunction.hxx

@@ -137,7 +137,7 @@ SingleImageCostFunction<TImage>
     }
 
   // Convert the image function output to the cost function derivative
-  const typename DerivativeType::ValueType DerivativeThreshold = 15.0;
+  constexpr typename DerivativeType::ValueType DerivativeThreshold  = 15.0;
   for (unsigned int i=0; i<ImageDimension; i++)
     {
     derivative[i] = static_cast<typename DerivativeType::ValueType>( output[i] );