ENH: Introduce itk::Boolean for use with std::vector

Modules/Core/Common/include/itkBoolean.h

@@ -0,0 +1,58 @@
+/*=========================================================================
+ *
+ *  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 itkBoolean_h
+#define itkBoolean_h
+
+namespace itk
+{
+
+/**
+ * \class Boolean
+ *
+ * \brief An alternative to bool for additional thread safety
+ *
+ * The class `Boolean` provides an alternative to `bool`. `std::vector<bool>` is not thread safe due to the possibility
+ * of multiple bits being packed together in the same memory location.  std::vector<Boolean> does not have such a space
+ * optimization. std::vector<Boolean> is semantically like `std::vector<bool>`, but unlike `std::vector<bool>`, it does
+ * "avoid data races when the contents of the contained object in different elements in the same container [...] are
+ * modified concurrently", according to the C++ Standard, section [container.requirements.dataraces], "Container data
+ * races".
+ *
+ * \ingroup ITKCommon
+ */
+class Boolean
+{
+public:
+  /** Supports default construction */
+  constexpr Boolean() = default;
+
+  /** Supports implicit conversion from `bool`. */
+  constexpr Boolean(bool v)
+    : m_Value(v)
+  {}
+
+  /** Supports implicit conversion to `bool`. */
+  constexpr operator bool() const { return m_Value; }
+
+private:
+  bool m_Value = false;
+};
+
+} // namespace itk
+
+#endif

Modules/Core/Common/include/itkBooleanStdVector.h

@@ -18,7 +18,7 @@
 #ifndef itkBooleanStdVector_h
 #define itkBooleanStdVector_h
 
-#include "itkIntTypes.h"
+#include "itkBoolean.h"
 #include <vector>
 
 namespace itk
@@ -30,11 +30,8 @@ namespace itk
  * `std::vector<bool>`, but unlike `std::vector<bool>`, it does "avoid data races when the contents of the contained
  * object in different elements in the same container [...] are modified concurrently", according to the C++ Standard,
  * section [container.requirements.dataraces], "Container data races".
- *
- * \note BooleanStdVectorType is only intended to be used for the storage of Boolean values (true and false), not for
- * arbitrary integer values.
  */
-using BooleanStdVectorType = std::vector<uint8_t>;
+using BooleanStdVectorType = std::vector<Boolean>;
 
 } // namespace itk
 

Modules/Core/Common/wrapping/ITKCommonBase.wrap

@@ -77,6 +77,7 @@ itk_wrap_simple_class("itk::OutputDataObjectIterator")
 itk_wrap_simple_class("itk::DataObjectConstIterator")
 itk_wrap_simple_class("itk::InputDataObjectConstIterator")
 itk_wrap_simple_class("itk::OutputDataObjectConstIterator")
+itk_wrap_simple_class("itk::Boolean")
 itk_wrap_simple_class("itk::Statistics::RandomVariateGeneratorBase" POINTER)
 itk_wrap_simple_class("itk::Statistics::MersenneTwisterRandomVariateGenerator" POINTER)