From 01e02019ab4d6381245cb650bfdf53bda417ec1d Mon Sep 17 00:00:00 2001
From: Niels Dekker <N.Dekker@lumc.nl>
Date: Tue, 30 Aug 2022 13:12:11 +0200
Subject: [PATCH] ENH: Mimic C++20 `std::make_unique_for_overwrite` for dynamic
 arrays

Allows creating a dynamically allocated array that is automatically deleted, by
calling `make_unique_for_overwrite<T[]>(numberOfElements)`.
---
 .../include/itkMakeUniqueForOverwrite.h       | 81 +++++++++++++++++++
 Modules/Core/Common/test/CMakeLists.txt       |  1 +
 .../test/itkMakeUniqueForOverwriteGTest.cxx   | 43 ++++++++++
 3 files changed, 125 insertions(+)
 create mode 100644 Modules/Core/Common/include/itkMakeUniqueForOverwrite.h
 create mode 100644 Modules/Core/Common/test/itkMakeUniqueForOverwriteGTest.cxx

diff --git a/Modules/Core/Common/include/itkMakeUniqueForOverwrite.h b/Modules/Core/Common/include/itkMakeUniqueForOverwrite.h
new file mode 100644
index 00000000000..9ff68cdb90d
--- /dev/null
+++ b/Modules/Core/Common/include/itkMakeUniqueForOverwrite.h
@@ -0,0 +1,81 @@
+/*=========================================================================
+ *
+ *  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
+ *
+ *         https://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 itkMakeUniqueForOverwrite_h
+#define itkMakeUniqueForOverwrite_h
+
+#include <memory> // For unique_ptr.
+
+#if __cplusplus < 202002L
+
+#  include <type_traits> // For remove_extent_t, false_type, etc.
+
+namespace itk
+{
+
+// Namespace of implementation details (not part of the public ITK interface).
+namespace MakeUniqueForOverwriteImplDetail
+{
+
+// `is_unbounded_array` implementation for C++14/C++17. From C++20, `std::is_unbounded_array` is preferred.
+template <typename>
+struct is_unbounded_array : std::false_type
+{};
+
+template <typename T>
+struct is_unbounded_array<T[]> : std::true_type
+{};
+
+} // namespace MakeUniqueForOverwriteImplDetail
+
+
+/** `make_unique_for_overwrite` implementation for C++14/C++17, specifically for dynamically sized ("unbounded")
+ * arrays. From C++20, `std::make_unique_for_overwrite` is preferred.
+ *
+ * Example (mind the square brackets):
+   \code
+     using ElementType = int;
+     size_t numberOfElements{ 42 };
+
+     // Create a buffer that may be used to store the specified number of elements.
+     auto buffer = make_unique_for_overwrite<ElementType[]>(numberOfElements);
+   \endcode
+ *
+ */
+template <typename TUnboundedArray>
+auto
+make_unique_for_overwrite(const size_t numberOfElements)
+{
+  // The template argument must be something like `ElementType[]`, having an empty pair of square brackets.
+  static_assert(MakeUniqueForOverwriteImplDetail::is_unbounded_array<TUnboundedArray>::value,
+                "The specified template argument must be an unbounded array type!");
+  return std::unique_ptr<TUnboundedArray>(new std::remove_extent_t<TUnboundedArray>[numberOfElements]);
+}
+
+} // namespace itk
+
+#else
+
+namespace itk
+{
+using ::std::make_unique_for_overwrite;
+}
+
+#endif
+
+#endif // itkMakeUniqueForOverwrite_h
diff --git a/Modules/Core/Common/test/CMakeLists.txt b/Modules/Core/Common/test/CMakeLists.txt
index a56212e4b60..0611d1cb694 100644
--- a/Modules/Core/Common/test/CMakeLists.txt
+++ b/Modules/Core/Common/test/CMakeLists.txt
@@ -638,6 +638,7 @@ set(ITKCommonGTests
       itkImageRegionGTest.cxx
       itkIndexGTest.cxx
       itkIndexRangeGTest.cxx
+      itkMakeUniqueForOverwriteGTest.cxx
       itkMatrixGTest.cxx
       itkMersenneTwisterRandomVariateGeneratorGTest.cxx
       itkNeighborhoodAllocatorGTest.cxx
diff --git a/Modules/Core/Common/test/itkMakeUniqueForOverwriteGTest.cxx b/Modules/Core/Common/test/itkMakeUniqueForOverwriteGTest.cxx
new file mode 100644
index 00000000000..96de252d9ed
--- /dev/null
+++ b/Modules/Core/Common/test/itkMakeUniqueForOverwriteGTest.cxx
@@ -0,0 +1,43 @@
+/*=========================================================================
+ *
+ *  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
+ *
+ *         https://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 "itkMakeUniqueForOverwrite.h"
+#include <gtest/gtest.h>
+#include <numeric> // For iota.
+
+
+// Tests that `make_unique_for_overwrite` creates an array of the specified dynamic size, whose elements can all be
+// written to.
+TEST(MakeUniqueForOverwrite, CreatesAnArrayThatCanBeWrittenTo)
+{
+  for (std::size_t numberOfElements = 1; numberOfElements < 4; ++numberOfElements)
+  {
+    const auto data = itk::make_unique_for_overwrite<int[]>(numberOfElements);
+    ASSERT_NE(data, nullptr);
+
+    // Write the values { 0, 1, ... , N-1 }.
+    std::iota(data.get(), data.get() + numberOfElements, 0);
+
+    // Check that each value is correctly written to the corresponding element.
+    for (std::size_t i = 0; i < numberOfElements; ++i)
+    {
+      EXPECT_EQ(data[i], i);
+    }
+  }
+}