Merge pull request #5703 from N-Dekker/FixedArray-empty

ENH: Add `FixedArray::empty()`, which always just returns false

Author: hjmjohnson

Modules/Core/Common/include/itkFixedArray.h

@@ -448,6 +448,12 @@ class ITK_TEMPLATE_EXPORT FixedArray
     return VLength;
   }
 
+  [[nodiscard]] constexpr bool
+  empty() const noexcept
+  {
+    return false;
+  }
+
   /** Set all the elements of the container to the input value. */
   void
   Fill(const ValueType &);

Modules/Core/Common/test/itkFixedArrayGTest.cxx

@@ -356,3 +356,15 @@ TEST(FixedArray, ValueInitialized)
   expectEachElementValueInitialized(itk::FixedArray<float, 3>{});
   expectEachElementValueInitialized(itk::FixedArray<void *, 3>{});
 }
+
+
+// Tests that empty() always returns false for FixedArray.
+TEST(FixedArray, EmptyIsFalse)
+{
+  static_assert(!itk::FixedArray<int>{}.empty());
+  static_assert(!itk::FixedArray<float, 1>{}.empty());
+  static_assert(!itk::FixedArray<void *, 2>{}.empty());
+  static_assert(!itk::FixedArray<double>::Filled(1.0).empty());
+
+  EXPECT_FALSE(itk::FixedArray<int>({ 0, 1, 2 }).empty());
+}