ENH: Add itk::MakeIndexRange functions, to ease creating an IndexRange

There are two kinds of IndexRange's: `ZeroBasedIndexRange` is optimized for an
image region that has a start index of all zeros. `ImageRegionIndexRange`
supports any arbitrary image region, having any arbitrary start index. The
overload set of `MakeIndexRange` functions aims to ease creating the most
appropriate IndexRange type:

 - `MakeIndexRange(size)` returns a `ZeroBasedIndexRange`
 - `MakeIndexRange(imageRegion)` returns an `ImageRegionIndexRange`
 - `MakeIndexRange(index, size)` returns an `ImageRegionIndexRange`

Adjusted the IndexRange unit tests and the Doxygen code example to use
`MakeIndexRange`.

Author: N-Dekker

Modules/Core/Common/include/itkIndexRange.h

@@ -41,9 +41,8 @@ namespace itk
     \code
     constexpr unsigned int Dimension{ 2 };
     const Size<Dimension> size = { {2, 3} };
-    const ZeroBasedIndexRange<Dimension> indexRange{ size };
 
-    for (const Index<Dimension> index : indexRange)
+    for (const Index<Dimension> index : MakeIndexRange(size))
     {
       std::cout << index;
     }
@@ -474,6 +473,30 @@ using ImageRegionIndexRange = IndexRange<VDimension, false>;
 template <unsigned int VDimension>
 using ZeroBasedIndexRange = IndexRange<VDimension, true>;
 
+/* Creates a range of indices for the specified grid size. */
+template <unsigned int VDimension>
+[[nodiscard]] constexpr auto
+MakeIndexRange(const Size<VDimension> & gridSize)
+{
+  return ZeroBasedIndexRange<VDimension>(gridSize);
+}
+
+/* Creates a range of indices for the specified image region. */
+template <unsigned int VDimension>
+[[nodiscard]] auto
+MakeIndexRange(const ImageRegion<VDimension> & imageRegion)
+{
+  return ImageRegionIndexRange<VDimension>(imageRegion);
+}
+
+/* Creates a range of indices for the image region specified by its index and size. */
+template <unsigned int VDimension>
+[[nodiscard]] auto
+MakeIndexRange(const Index<VDimension> & imageRegionIndex, const Size<VDimension> & imageRegionSize)
+{
+  return ImageRegionIndexRange<VDimension>(ImageRegion<VDimension>{ imageRegionIndex, imageRegionSize });
+}
+
 } // namespace itk
 
 #endif

Modules/Core/Common/test/itkIndexRangeGTest.cxx

@@ -35,13 +35,26 @@ template class itk::IndexRange<2, false>;
 
 using itk::IndexRange;
 using itk::ImageRegionIndexRange;
+using itk::MakeIndexRange;
 using itk::ZeroBasedIndexRange;
 using itk::RangeGTestUtilities;
 
 
 static_assert(sizeof(ZeroBasedIndexRange<3>) < sizeof(ImageRegionIndexRange<3>),
               "ZeroBasedIndexRange does not need to store the index of a region, so it should take less memory.");
 
+static_assert(std::is_same_v<decltype(MakeIndexRange(itk::Size<2>{})), ZeroBasedIndexRange<2>> &&
+                std::is_same_v<decltype(MakeIndexRange(itk::Size<3>{})), ZeroBasedIndexRange<3>>,
+              "MakeIndexRange(size) should return a ZeroBasedIndexRange.");
+
+static_assert(std::is_same_v<decltype(MakeIndexRange(itk::ImageRegion<2>{})), ImageRegionIndexRange<2>> &&
+                std::is_same_v<decltype(MakeIndexRange(itk::ImageRegion<3>{})), ImageRegionIndexRange<3>>,
+              "MakeIndexRange(imageRegion) should return an ImageRegionIndexRange.");
+
+static_assert(std::is_same_v<decltype(MakeIndexRange(itk::Index<2>{}, itk::Size<2>{})), ImageRegionIndexRange<2>> &&
+                std::is_same_v<decltype(MakeIndexRange(itk::Index<3>{}, itk::Size<3>{})), ImageRegionIndexRange<3>>,
+              "MakeIndexRange(index, size) should return an ImageRegionIndexRange.");
+
 namespace
 {
 template <unsigned int VDimension>
@@ -107,7 +120,9 @@ ExpectRangeIsEmptyWhenRegionSizeIsZero(std::mt19937 & randomNumberEngine)
   const itk::Index<VDimension>       randomRegionIndex = GenerateRandomIndex<VDimension>(randomNumberEngine);
   const itk::ImageRegion<VDimension> zeroSizedImageRegion{ randomRegionIndex, zeroSize };
 
-  EXPECT_TRUE(ImageRegionIndexRange<VDimension>{ zeroSizedImageRegion }.empty());
+  EXPECT_TRUE(MakeIndexRange(zeroSize).empty());
+  EXPECT_TRUE(MakeIndexRange(zeroSizedImageRegion).empty());
+  EXPECT_TRUE(MakeIndexRange(randomRegionIndex, zeroSize).empty());
 }