text: ///////////////////////////////////////////////////////////////////////////
  //
  // Copyright (c) DreamWorks Animation LLC
  //
  // All rights reserved. This software is distributed under the
  // Mozilla Public License 2.0 ( http://www.mozilla.org/MPL/2.0/ )
  //
  // Redistributions of source code must retain the above copyright
  // and license notice and the following restrictions and disclaimer.
  //
  // *     Neither the name of DreamWorks Animation nor the names of
  // its contributors may be used to endorse or promote products derived
  // from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY INDIRECT, INCIDENTAL,
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  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  // IN NO EVENT SHALL THE COPYRIGHT HOLDERS' AND CONTRIBUTORS' AGGREGATE
  // LIABILITY FOR ALL CLAIMS REGARDLESS OF THEIR BASIS EXCEED US$250.00.
  //
  ///////////////////////////////////////////////////////////////////////////
  
  /// @file NodeUnion.h
  ///
  /// @details NodeUnion is a templated helper class that controls access to either
  /// the child node pointer or the value for a particular element of a root
  /// or internal node. For space efficiency, the child pointer and the value
  /// are unioned when possible, since the two are never in use simultaneously.
  
  #ifndef OPENVDB_TREE_NODEUNION_HAS_BEEN_INCLUDED
  #define OPENVDB_TREE_NODEUNION_HAS_BEEN_INCLUDED
  
  #include <openvdb/version.h>
  #include <openvdb/Types.h>
  #include <cstring> // for std::memcpy()
  #include <type_traits>
  
  namespace openvdb {
  OPENVDB_USE_VERSION_NAMESPACE
  namespace OPENVDB_VERSION_NAME {
  namespace tree {
  
  #if OPENVDB_ABI_VERSION_NUMBER >= 4
  
  // Forward declaration of traits class
  template<typename T> struct CopyTraits;
  
  // Default implementation that stores the child pointer and the value separately
  // (i.e., not in a union)
  // This implementation is not used for POD, math::Vec or math::Coord value types.
  template<typename ValueT, typename ChildT, typename Enable = void>
  class NodeUnion
  {
  private:
      ChildT* mChild;
      ValueT  mValue;
  
  public:
      NodeUnion(): mChild(nullptr), mValue() {}
  
      ChildT* getChild() const { return mChild; }
      void setChild(ChildT* child) { mChild = child; }
  
      const ValueT& getValue() const { return mValue; }
      ValueT& getValue() { return mValue; }
      void setValue(const ValueT& val) { mValue = val; }
  };
  
  
  // Template specialization for values of POD types (int, float, pointer, etc.)
  template<typename ValueT, typename ChildT>
  class NodeUnion<ValueT, ChildT, typename std::enable_if<std::is_pod<ValueT>::value>::type>
  {
  private:
      union { ChildT* mChild; ValueT mValue; };
  
  public:
      NodeUnion(): mChild(nullptr) {}
  
      ChildT* getChild() const { return mChild; }
      void setChild(ChildT* child) { mChild = child; }
  
      const ValueT& getValue() const { return mValue; }
      ValueT& getValue() { return mValue; }
      void setValue(const ValueT& val) { mValue = val; }
  };
  
  
  // Template specialization for values of types such as math::Vec3f and math::Coord
  // for which CopyTraits<T>::IsCopyable is true
  template<typename ValueT, typename ChildT>
  class NodeUnion<ValueT, ChildT, typename std::enable_if<CopyTraits<ValueT>::IsCopyable>::type>
  {
  private:
      union { ChildT* mChild; ValueT mValue; };
  
  public:
      NodeUnion(): mChild(nullptr) {}
      NodeUnion(const NodeUnion& other): mChild(nullptr)
          { std::memcpy(this, &other, sizeof(*this)); }
      NodeUnion& operator=(const NodeUnion& rhs)
          { std::memcpy(this, &rhs, sizeof(*this)); return *this; }
  
      ChildT* getChild() const { return mChild; }
      void setChild(ChildT* child) { mChild = child; }
  
      const ValueT& getValue() const { return mValue; }
      ValueT& getValue() { return mValue; }
      void setValue(const ValueT& val) { mValue = val; }
  };
  
  
  /// @details A type T is copyable if
  /// # T stores member values by value (vs. by pointer or reference)
  ///   and T's true byte size is given by sizeof(T).
  /// # T has a trivial destructor
  /// # T has a default constructor
  /// # T has an assignment operator
  template<typename T> struct CopyTraits { static const bool IsCopyable = false; };
  template<typename T> struct CopyTraits<math::Vec2<T>> { static const bool IsCopyable = true; };
  template<typename T> struct CopyTraits<math::Vec3<T>> { static const bool IsCopyable = true; };
  template<typename T> struct CopyTraits<math::Vec4<T>> { static const bool IsCopyable = true; };
  template<> struct CopyTraits<math::Coord> { static const bool IsCopyable = true; };
  
  
  ////////////////////////////////////////
  
  
  #else // OPENVDB_ABI_VERSION_NUMBER <= 3
  
  // Prior to OpenVDB 4 and the introduction of C++11, values of non-POD types
  // were heap-allocated and stored by pointer due to C++98 restrictions on unions.
  
  // Internal implementation of a union of a child node pointer and a value
  template<bool ValueIsClass, class ValueT, class ChildT> class NodeUnionImpl;
  
  
  // Partial specialization for values of non-class types
  // (int, float, pointer, etc.) that stores elements by value
  template<typename ValueT, typename ChildT>
  class NodeUnionImpl</*ValueIsClass=*/false, ValueT, ChildT>
  {
  private:
      union { ChildT* child; ValueT value; } mUnion;
  
  public:
      NodeUnionImpl() { mUnion.child = nullptr; }
  
      ChildT* getChild() const { return mUnion.child; }
      void setChild(ChildT* child) { mUnion.child = child; }
  
      const ValueT& getValue() const { return mUnion.value; }
      ValueT& getValue() { return mUnion.value; }
      void setValue(const ValueT& val) { mUnion.value = val; }
  };
  
  
  // Partial specialization for values of class types (std::string,
  // math::Vec, etc.) that stores elements by pointer
  template<typename ValueT, typename ChildT>
  class NodeUnionImpl</*ValueIsClass=*/true, ValueT, ChildT>
  {
  private:
      union { ChildT* child; ValueT* value; } mUnion;
      bool mHasChild;
  
  public:
      NodeUnionImpl() : mHasChild(true) { this->setChild(nullptr); }
      NodeUnionImpl(const NodeUnionImpl& other) : mHasChild(true)
      {
          if (other.mHasChild) {
              this->setChild(other.getChild());
          } else {
              this->setValue(other.getValue());
          }
      }
      NodeUnionImpl& operator=(const NodeUnionImpl& other)
      {
          if (other.mHasChild) {
              this->setChild(other.getChild());
          } else {
              this->setValue(other.getValue());
          }
          return *this;
      }
      ~NodeUnionImpl() { this->setChild(nullptr); }
  
      ChildT* getChild() const { return mHasChild ? mUnion.child : nullptr; }
      void setChild(ChildT* child)
      {
          if (!mHasChild) delete mUnion.value;
          mUnion.child = child;
          mHasChild = true;
      }
  
      const ValueT& getValue() const { return *mUnion.value; }
      ValueT& getValue() { return *mUnion.value; }
      void setValue(const ValueT& val)
      {
          if (!mHasChild) delete mUnion.value;
          mUnion.value = new ValueT(val);
          mHasChild = false;
      }
  };
  
  
  template<typename ValueT, typename ChildT>
  struct NodeUnion: public NodeUnionImpl<std::is_class<ValueT>::value, ValueT, ChildT>
  {
      NodeUnion() {}
  };
  
  #endif
  
  } // namespace tree
  } // namespace OPENVDB_VERSION_NAME
  } // namespace openvdb
  
  #endif // OPENVDB_TREE_NODEUNION_HAS_BEEN_INCLUDED
  
  // Copyright (c) DreamWorks Animation LLC
  // All rights reserved. This software is distributed under the
  // Mozilla Public License 2.0 ( http://www.mozilla.org/MPL/2.0/ )
  