Add constexpr begin(), end(), cbegin(), cend() to FixedArray, Index, Offset, and Size

Modules/Core/Common/include/itkFixedArray.h

@@ -322,37 +322,37 @@ class ITK_TEMPLATE_EXPORT FixedArray
 
   itkLegacyMacro(ConstReverseIterator rEnd() const);
 
-  const_iterator
+  constexpr const_iterator
   cbegin() const noexcept
   {
     return m_InternalArray;
   }
 
-  iterator
+  constexpr iterator
   begin() noexcept
   {
     return m_InternalArray;
   }
 
-  const_iterator
+  constexpr const_iterator
   begin() const noexcept
   {
     return this->cbegin();
   }
 
-  const_iterator
+  constexpr const_iterator
   cend() const noexcept
   {
     return m_InternalArray + VLength;
   }
 
-  iterator
+  constexpr iterator
   end() noexcept
   {
     return m_InternalArray + VLength;
   }
 
-  const_iterator
+  constexpr const_iterator
   end() const noexcept
   {
     return this->cend();

Modules/Core/Common/include/itkIndex.h

@@ -346,28 +346,40 @@ struct ITK_TEMPLATE_EXPORT Index final
     std::swap(m_InternalArray, other.m_InternalArray);
   }
 
-  iterator
+  constexpr const_iterator
+  cbegin() const
+  {
+    return &m_InternalArray[0];
+  }
+
+  constexpr iterator
   begin()
   {
-    return iterator(&m_InternalArray[0]);
+    return &m_InternalArray[0];
   }
 
-  const_iterator
+  constexpr const_iterator
   begin() const
   {
-    return const_iterator(&m_InternalArray[0]);
+    return &m_InternalArray[0];
+  }
+
+  constexpr const_iterator
+  cend() const
+  {
+    return &m_InternalArray[VDimension];
   }
 
-  iterator
+  constexpr iterator
   end()
   {
-    return iterator(&m_InternalArray[VDimension]);
+    return &m_InternalArray[VDimension];
   }
 
-  const_iterator
+  constexpr const_iterator
   end() const
   {
-    return const_iterator(&m_InternalArray[VDimension]);
+    return &m_InternalArray[VDimension];
   }
 
   reverse_iterator

Modules/Core/Common/include/itkOffset.h

@@ -299,28 +299,40 @@ struct ITK_TEMPLATE_EXPORT Offset final
     std::swap(m_InternalArray, other.m_InternalArray);
   }
 
-  iterator
+  constexpr const_iterator
+  cbegin() const
+  {
+    return &m_InternalArray[0];
+  }
+
+  constexpr iterator
   begin()
   {
-    return iterator(&m_InternalArray[0]);
+    return &m_InternalArray[0];
   }
 
-  const_iterator
+  constexpr const_iterator
   begin() const
   {
-    return const_iterator(&m_InternalArray[0]);
+    return &m_InternalArray[0];
+  }
+
+  constexpr const_iterator
+  cend() const
+  {
+    return &m_InternalArray[VDimension];
   }
 
-  iterator
+  constexpr iterator
   end()
   {
-    return iterator(&m_InternalArray[VDimension]);
+    return &m_InternalArray[VDimension];
   }
 
-  const_iterator
+  constexpr const_iterator
   end() const
   {
-    return const_iterator(&m_InternalArray[VDimension]);
+    return &m_InternalArray[VDimension];
   }
 
   reverse_iterator

Modules/Core/Common/include/itkSize.h

@@ -258,28 +258,40 @@ struct ITK_TEMPLATE_EXPORT Size final
     std::swap(m_InternalArray, other.m_InternalArray);
   }
 
-  iterator
+  constexpr const_iterator
+  cbegin() const
+  {
+    return &m_InternalArray[0];
+  }
+
+  constexpr iterator
   begin()
   {
-    return iterator(&m_InternalArray[0]);
+    return &m_InternalArray[0];
   }
 
-  const_iterator
+  constexpr const_iterator
   begin() const
   {
-    return const_iterator(&m_InternalArray[0]);
+    return &m_InternalArray[0];
+  }
+
+  constexpr const_iterator
+  cend() const
+  {
+    return &m_InternalArray[VDimension];
   }
 
-  iterator
+  constexpr iterator
   end()
   {
-    return iterator(&m_InternalArray[VDimension]);
+    return &m_InternalArray[VDimension];
   }
 
-  const_iterator
+  constexpr const_iterator
   end() const
   {
-    return const_iterator(&m_InternalArray[VDimension]);
+    return &m_InternalArray[VDimension];
   }
 
   reverse_iterator

Modules/Core/Common/test/CMakeLists.txt

@@ -624,6 +624,7 @@ set(ITKCommonGTests
       itkMersenneTwisterRandomVariateGeneratorGTest.cxx
       itkNeighborhoodAllocatorGTest.cxx
       itkNumberToStringGTest.cxx
+      itkOffsetGTest.cxx
       itkOptimizerParametersGTest.cxx
       itkPointGTest.cxx
       itkShapedImageNeighborhoodRangeGTest.cxx

Modules/Core/Common/test/itkFixedArrayGTest.cxx

@@ -21,6 +21,7 @@
 
 // First include the header file to be tested:
 #include "itkFixedArray.h"
+#include "itkRangeGTestUtilities.h"
 #include <gtest/gtest.h>
 
 #include <array>
@@ -248,6 +249,10 @@ static_assert(Is_Filled_FixedArray_correctly_filled<0>() && Is_Filled_FixedArray
                 Is_Filled_FixedArray_correctly_filled<std::numeric_limits<int>::max()>(),
               "itk::FixedArray::Filled(value) should be correctly filled at compile-time");
 
+static_assert(itk::RangeGTestUtilities::CheckConstexprBeginAndEndOfContainer<itk::FixedArray<int>>() &&
+                itk::RangeGTestUtilities::CheckConstexprBeginAndEndOfContainer<itk::FixedArray<double, 1>>(),
+              "Check constexpr begin() and end() of FixedArray.");
+
 
 // Tests that the values of a FixedArray (either const or non-const) can be retrieved by a
 // range-based for-loop.

Modules/Core/Common/test/itkIndexGTest.cxx

@@ -18,6 +18,7 @@
 
 // First include the header file to be tested:
 #include "itkIndex.h"
+#include "itkRangeGTestUtilities.h"
 #include <gtest/gtest.h>
 #include <initializer_list>
 #include <limits>
@@ -70,6 +71,10 @@ static_assert(Is_Filled_Index_correctly_filled<0>() && Is_Filled_Index_correctly
                 Is_Filled_Index_correctly_filled<std::numeric_limits<itk::IndexValueType>::max()>(),
               "itk::Index::Filled(value) should be correctly filled at compile-time");
 
+static_assert(itk::RangeGTestUtilities::CheckConstexprBeginAndEndOfContainer<itk::Index<>>() &&
+                itk::RangeGTestUtilities::CheckConstexprBeginAndEndOfContainer<itk::Index<1>>(),
+              "Check constexpr begin() and end() of Index.");
+
 
 // Tests that itk::Index::Filled(value) returns an itk::Index with the
 // specified value for each element.

Modules/Core/Common/test/itkOffsetGTest.cxx

@@ -0,0 +1,26 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+// First include the header file to be tested:
+#include "itkOffset.h"
+#include "itkRangeGTestUtilities.h"
+
+
+static_assert(itk::RangeGTestUtilities::CheckConstexprBeginAndEndOfContainer<itk::Offset<>>() &&
+                itk::RangeGTestUtilities::CheckConstexprBeginAndEndOfContainer<itk::Offset<1>>(),
+              "Check constexpr begin() and end() of Offset.");

Modules/Core/Common/test/itkRangeGTestUtilities.h

@@ -103,6 +103,40 @@ class RangeGTestUtilities
     ExpectRangesHaveEqualBeginAndEnd(moveAssignedRange, originalRangeBeforeMove);
   }
 
+
+  // Checks the `constexpr` member functions begin() and end() of a container like FixedArray, Index, Offset and Size.
+  template <typename TContainer>
+  static constexpr bool
+  CheckConstexprBeginAndEndOfContainer()
+  {
+    using ConstContainerType = const TContainer;
+    using ValueType = std::remove_reference_t<decltype(*(TContainer().begin()))>;
+
+    static_assert(std::is_same<decltype(*(TContainer().begin())), ValueType &>::value,
+                  "For a non-const container, begin() should return a non-const reference");
+    static_assert(std::is_same<decltype(*(ConstContainerType().begin())), const ValueType &>::value,
+                  "For a const container, begin() should return a const reference");
+    static_assert(std::is_same<decltype(*(TContainer().cbegin())), const ValueType &>::value &&
+                    std::is_same<decltype(*(ConstContainerType().cbegin())), const ValueType &>::value,
+                  "For any container, cbegin() should return a const reference");
+
+    static_assert(std::is_same<decltype(*(TContainer().end())), ValueType &>::value,
+                  "For a non-const container, end() should return a non-const reference");
+    static_assert(std::is_same<decltype(*(ConstContainerType().end())), const ValueType &>::value,
+                  "For a const container, end() should return a const reference");
+    static_assert(std::is_same<decltype(*(TContainer().cend())), const ValueType &>::value &&
+                    std::is_same<decltype(*(ConstContainerType().cend())), const ValueType &>::value,
+                  "For any container, cend() should return a const reference");
+
+    constexpr TContainer container{};
+
+    static_assert(container.cbegin() == container.begin(), "cbegin() should return the same iterator as begin().");
+    static_assert(container.cend() == container.end(), "cend() should return the same iterator as end().");
+
+    // Just return true to ease calling this function inside a static_assert.
+    return true;
+  }
+
 private:
   template <typename TRange>
   static void

Modules/Core/Common/test/itkSizeGTest.cxx

@@ -18,6 +18,7 @@
 
 // First include the header file to be tested:
 #include "itkSize.h"
+#include "itkRangeGTestUtilities.h"
 #include <gtest/gtest.h>
 #include <limits>
 #include <type_traits> // For integral_constant.
@@ -75,6 +76,10 @@ static_assert(Is_Filled_Size_correctly_filled<0>() && Is_Filled_Size_correctly_f
                 Is_Filled_Size_correctly_filled<std::numeric_limits<itk::IndexValueType>::max()>(),
               "itk::Size::Filled(value) should be correctly filled at compile-time");
 
+static_assert(itk::RangeGTestUtilities::CheckConstexprBeginAndEndOfContainer<itk::Size<>>() &&
+                itk::RangeGTestUtilities::CheckConstexprBeginAndEndOfContainer<itk::Size<1>>(),
+              "Check constexpr begin() and end() of Size.");
+
 
 // Tests that itk::Size::Filled(value) returns an itk::Size with the
 // specified value for each element.