From b058df79b2ce3ab134f921104e17ab2611b1fba1 Mon Sep 17 00:00:00 2001
From: Bradley Lowekamp <blowekamp@mail.nih.gov>
Date: Mon, 26 Aug 2024 09:34:02 -0400
Subject: [PATCH] STYLE: move details to MetaDataObjectDetail

Move meta programming details from unnamed namespace to separate file
and header.
---
 .../Core/Common/include/itkMetaDataObject.hxx | 25 ++--------
 .../Common/include/itkMetaDataObjectDetail.h  | 50 +++++++++++++++++++
 2 files changed, 53 insertions(+), 22 deletions(-)
 create mode 100644 Modules/Core/Common/include/itkMetaDataObjectDetail.h

diff --git a/Modules/Core/Common/include/itkMetaDataObject.hxx b/Modules/Core/Common/include/itkMetaDataObject.hxx
index 47c2d548956..27ec13a373b 100644
--- a/Modules/Core/Common/include/itkMetaDataObject.hxx
+++ b/Modules/Core/Common/include/itkMetaDataObject.hxx
@@ -28,6 +28,7 @@
 #ifndef itkMetaDataObject_hxx
 #define itkMetaDataObject_hxx
 
+#include "itkMetaDataObjectDetail.h"
 
 namespace itk
 {
@@ -59,26 +60,6 @@ MetaDataObject<MetaDataObjectType>::SetMetaDataObjectValue(const MetaDataObjectT
   Self::Assign(m_MetaDataObjectValue, newValue);
 }
 
-namespace
-{
-template <class T, class = void>
-struct has_Print : std::false_type
-{};
-
-template <class T>
-struct has_Print<T, std::void_t<decltype(std::declval<T>().Print(std::declval<std::ostream &>()))>> : std::true_type
-{};
-
-template <class T, class = void>
-struct has_output_operator : std::false_type
-{};
-
-template <class T>
-struct has_output_operator<T, std::void_t<decltype(std::declval<std::ostream &>() << std::declval<T>())>>
-  : std::true_type
-{};
-} // namespace
-
 template <typename MetaDataObjectType>
 void
 MetaDataObject<MetaDataObjectType>::Print(std::ostream & os) const
@@ -86,11 +67,11 @@ MetaDataObject<MetaDataObjectType>::Print(std::ostream & os) const
   // future c++20 feature
   // constexpr bool hasPrint = false; requires( const &MetaDataObjectType obj ) { obj.Print(os); };
 
-  if constexpr (has_Print<MetaDataObjectType>::value)
+  if constexpr (MetaDataObjectDetail::has_Print<MetaDataObjectType>::value)
   {
     m_MetaDataObjectValue.Print(os);
   }
-  else if constexpr (has_output_operator<MetaDataObjectType>::value)
+  else if constexpr (MetaDataObjectDetail::has_output_operator<MetaDataObjectType>::value)
   {
     os << m_MetaDataObjectValue;
   }
diff --git a/Modules/Core/Common/include/itkMetaDataObjectDetail.h b/Modules/Core/Common/include/itkMetaDataObjectDetail.h
new file mode 100644
index 00000000000..38b140fde03
--- /dev/null
+++ b/Modules/Core/Common/include/itkMetaDataObjectDetail.h
@@ -0,0 +1,50 @@
+/*=========================================================================
+ *
+ *  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 itkMetaDataObjectDetail_h
+#define itkMetaDataObjectDetail_h
+
+#include <type_traits>
+#include <utility>
+
+namespace itk
+{
+
+// Implementation details for MetaDataObject meta programming
+namespace MetaDataObjectDetail
+{
+template <class T, class = void>
+struct has_Print : std::false_type
+{};
+
+template <class T>
+struct has_Print<T, std::void_t<decltype(std::declval<T>().Print(std::declval<std::ostream &>()))>> : std::true_type
+{};
+
+template <class T, class = void>
+struct has_output_operator : std::false_type
+{};
+
+template <class T>
+struct has_output_operator<T, std::void_t<decltype(std::declval<std::ostream &>() << std::declval<T>())>>
+  : std::true_type
+{};
+} // namespace MetaDataObjectDetail
+} // namespace itk
+
+#endif