ENH: deprecate itk::EnableIf and the header which implements it

It should be replaced by std::enable_if from STL.

Author: dzenanz

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

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

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

Modules/Core/Common/test/itkEnableIfTest.cxx

@@ -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",