Merge pull request InsightSoftwareConsortium#5709 from N-Dekker/FixedArray-front-back

Author: dzenanz

Modules/Core/Common/include/itkFixedArray.h

@@ -313,6 +313,31 @@ class ITK_TEMPLATE_EXPORT FixedArray
     return m_InternalArray[index];
   }
   /** @ITKEndGrouping */
+
+  [[nodiscard]] constexpr reference
+  front()
+  {
+    return m_InternalArray[0];
+  }
+
+  [[nodiscard]] constexpr const_reference
+  front() const
+  {
+    return m_InternalArray[0];
+  }
+
+  [[nodiscard]] constexpr reference
+  back()
+  {
+    return m_InternalArray[VLength - 1];
+  }
+
+  [[nodiscard]] constexpr const_reference
+  back() const
+  {
+    return m_InternalArray[VLength - 1];
+  }
+
   /** Return a pointer to the data. */
   ValueType *
   GetDataPointer()

Modules/Core/Common/test/itkFixedArrayGTest.cxx

@@ -368,3 +368,12 @@ TEST(FixedArray, EmptyIsFalse)
 
   EXPECT_FALSE(itk::FixedArray<int>({ 0, 1, 2 }).empty());
 }
+
+
+// Tests front() and back().
+TEST(FixedArray, CheckFrontAndBack)
+{
+  itk::RangeGTestUtilities::CheckFrontAndBack(itk::FixedArray<int, 1>{});
+  itk::RangeGTestUtilities::CheckFrontAndBack(itk::FixedArray<int>({ 0, 1, 2 }));
+  itk::RangeGTestUtilities::CheckFrontAndBack(itk::FixedArray<double>::Filled(std::numeric_limits<double>::max()));
+}

Modules/Core/Common/test/itkRangeGTestUtilities.h

@@ -223,6 +223,22 @@ class RangeGTestUtilities
   }
 
 
+  template <typename TRange>
+  static void
+  CheckFrontAndBack(TRange && range)
+  {
+    ASSERT_FALSE(std::empty(range));
+
+    // Check that front() is at the begin, and back() is just before the end.
+    EXPECT_EQ(&range.front(), &*std::cbegin(range));
+    EXPECT_EQ(&range.back(), &*std::prev(std::cend(range)));
+
+    // Check that const and non-const overloads return a reference to the same element.
+    EXPECT_EQ(&std::as_const(range).front(), &range.front());
+    EXPECT_EQ(&std::as_const(range).back(), &range.back());
+  }
+
+
   // Checks that each element of the specified range is zero.
   template <typename TRange>
   static void