ENH: Add itk::MakeFilled<TContainer>(value), requested by issue #3230

Discussed extensively at issue #3230
"Create templated function `MakeFilled`", submitted by Lee Newberg in response to
issue #3006
"Cannot set image spacing via SpacingType::Filled", by Dženan Zukić.

Modules/Core/Common/include/itkMakeFilled.h

@@ -0,0 +1,46 @@
+/*=========================================================================
+ *
+ *  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.
+ *
+ *=========================================================================*/
+#ifndef itkMakeFilled_h
+#define itkMakeFilled_h
+
+namespace itk
+{
+/** Yields a container of the specified type, filled by the specified value, assigned to each of its elements.
+ * Only intended for container types of a compile-time fixed size, including instances of FixedArray (and derived
+ * classes), Index, Offset, Size, and std::array. Moreover, their size (number of elements) should be greater than zero.
+ */
+template <typename TContainer>
+constexpr TContainer
+MakeFilled(typename TContainer::const_reference value)
+{
+  // Note: The seemingly redundant {} initialization is required for C++14 and C++17, in order to declare MakeFilled
+  // constexpr. (C++20 does allow uninitialized variables in a constexpr function.)
+  TContainer container{};
+
+  static_assert(container.size() > 0, "MakeFilled requires TContainer with constant non-zero size!");
+
+  // Note that `std::fill` and `std::fill_n` are not `constexpr` until C++20.
+  for (auto & element : container)
+  {
+    element = value;
+  }
+  return container;
+}
+} // namespace itk
+
+#endif // itkMakeFilled_h