From 9f3a6243bf8025dd2fa122199b8d24ee5e00e3de Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?D=C5=BEenan=20Zuki=C4=87?= <dzenan.zukic@kitware.com>
Date: Fri, 3 Sep 2021 19:31:13 -0400
Subject: [PATCH] ENH: deprecate itk::EnableIf and the header which implements
 it

It should be replaced by std::enable_if from STL.
---
 Documentation/ITK5MigrationGuide.md          |   1 +
 Modules/Core/Common/include/itkEnableIf.h    |   8 ++
 Modules/Core/Common/test/CMakeLists.txt      |   1 -
 Modules/Core/Common/test/itkEnableIfTest.cxx | 107 -------------------
 Utilities/Maintenance/BuildHeaderTest.py     |   1 +
 5 files changed, 10 insertions(+), 108 deletions(-)
 delete mode 100644 Modules/Core/Common/test/itkEnableIfTest.cxx

diff --git a/Documentation/ITK5MigrationGuide.md b/Documentation/ITK5MigrationGuide.md
index 1f8ad649bb5..a5b06b04d9b 100644
--- a/Documentation/ITK5MigrationGuide.md
+++ b/Documentation/ITK5MigrationGuide.md
@@ -79,6 +79,7 @@ To modernize your code base, replace:
   * `SimpleFastMutexLock` with `std::mutex`, and `#include "itkSimpleFastMutexLock.h"`  with `#include <mutex>`.
   * `FastMutexLock` with `std::mutex`, and `#include "itkFastMutexLock.h"`  with `#include <mutex>`.
   * `MutexLock` with `std::mutex`, and `#include "itkMutexLock.h"`  with `#include <mutex>`.
+  * `mpl::EnableIf<X>::Type` with `std::enable_if_t<X>`, and `#include "itkEnableIf.h"` with `#include <type_traits>`.
 
 
 Modern CMake requirement
diff --git a/Modules/Core/Common/include/itkEnableIf.h b/Modules/Core/Common/include/itkEnableIf.h
index fed23d28532..38924f5481d 100644
--- a/Modules/Core/Common/include/itkEnableIf.h
+++ b/Modules/Core/Common/include/itkEnableIf.h
@@ -18,6 +18,10 @@
 #ifndef itkEnableIf_h
 #define itkEnableIf_h
 
+#include "itkMacro.h"
+
+#if !defined(ITK_LEGACY_REMOVE)
+
 namespace itk
 {
 /// \cond HIDE_META_PROGRAMMING
@@ -159,4 +163,8 @@ using mpl::DisableIfC;
 /// \endcond
 } // namespace itk
 
+#else // ITK_LEGACY_REMOVE
+#  error Use C++ 11 std::enable_if directly
+#endif
+
 #endif // itkEnableIf_h
diff --git a/Modules/Core/Common/test/CMakeLists.txt b/Modules/Core/Common/test/CMakeLists.txt
index 2692cf1528b..35620bca882 100644
--- a/Modules/Core/Common/test/CMakeLists.txt
+++ b/Modules/Core/Common/test/CMakeLists.txt
@@ -173,7 +173,6 @@ itkOptimizerParametersTest.cxx
 itkImageVectorOptimizerParametersHelperTest.cxx
 itkCompensatedSummationTest.cxx
 itkCompensatedSummationTest2.cxx
-itkEnableIfTest.cxx
 itkImageRegionConstIteratorWithOnlyIndexTest.cxx
 itkImageRandomConstIteratorWithOnlyIndexTest.cxx
 itkConstNeighborhoodIteratorWithOnlyIndexTest.cxx
diff --git a/Modules/Core/Common/test/itkEnableIfTest.cxx b/Modules/Core/Common/test/itkEnableIfTest.cxx
deleted file mode 100644
index 2ef5593103c..00000000000
--- a/Modules/Core/Common/test/itkEnableIfTest.cxx
+++ /dev/null
@@ -1,107 +0,0 @@
-/*=========================================================================
- *
- *  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.
- *
- *=========================================================================*/
-
-#include "itkEnableIf.h"
-#include "itkIsSame.h"
-#include "itkNumericTraits.h"
-#include "itkFixedArray.h"
-#include <cstdlib>
-#include <iostream>
-
-namespace
-{
-
-template <unsigned int D>
-typename itk::EnableIfC<D == 1>::Type
-test1()
-{
-  std::cout << "D is one" << std::endl;
-}
-
-template <unsigned int D>
-typename itk::EnableIfC<D != 1>::Type
-test1()
-{
-  std::cout << "D is not one" << std::endl;
-}
-
-template <typename T>
-typename itk::EnableIfC<sizeof(T) == 1>::Type
-test2()
-{
-  std::cout << "T is one in size" << std::endl;
-}
-
-template <typename T>
-typename itk::EnableIfC<sizeof(T) != 1>::Type
-test2()
-{
-  std::cout << "T is not one in size" << std::endl;
-}
-
-
-template <typename T>
-typename itk::EnableIfC<itk::IsSame<T, typename itk::NumericTraits<T>::ValueType>::Value>::Type
-test3()
-{
-  std::cout << "T is enabled" << std::endl;
-}
-
-template <typename T>
-typename itk::DisableIfC<itk::IsSame<T, typename itk::NumericTraits<T>::ValueType>::Value>::Type
-test3()
-{
-  std::cout << "T is disabled" << std::endl;
-}
-
-template <typename T>
-typename itk::EnableIfC<itk::IsSame<T, typename itk::NumericTraits<T>::ValueType>::Value>::Type
-test4(const T &)
-{
-  std::cout << "T is enabled" << std::endl;
-}
-
-template <typename T>
-typename itk::DisableIfC<itk::IsSame<T, typename itk::NumericTraits<T>::ValueType>::Value>::Type
-test4(const T &)
-{
-  std::cout << "T is disabled" << std::endl;
-}
-
-
-} // namespace
-
-int
-itkEnableIfTest(int, char *[])
-{
-
-  test1<0>();
-  test1<1>();
-  test1<2>();
-
-  test2<char>();
-  test2<int>();
-  test2<void *>();
-
-  test3<int>();
-  test3<itk::FixedArray<double, 3>>();
-
-  test4(1);
-  test4(itk::FixedArray<double, 3>());
-  return EXIT_SUCCESS;
-}
diff --git a/Utilities/Maintenance/BuildHeaderTest.py b/Utilities/Maintenance/BuildHeaderTest.py
index 93fd1b9b66d..a7280bfca2b 100755
--- a/Utilities/Maintenance/BuildHeaderTest.py
+++ b/Utilities/Maintenance/BuildHeaderTest.py
@@ -48,6 +48,7 @@
         "itkBSplineDeformableTransform.h",  # deprecated
         "vtkCaptureScreen.h",  # these includes require VTK
         "itkMultiThreader.h",  # Compatibility file, it should not be used
+        "itkEnableIf.h", # Compatibility file, it should not be used
         "itkViewImage.h",  # Depends on VTK_RENDERING_BACKEND
         "QuickView.h",  # Depends on VTK_RENDERING_BACKEND
         "itkBSplineDeformableTransformInitializer.h",