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+// -*- C++ -*-
+
+//==========================================================================
+/**
+ * @file Value_Ptr.h
+ *
+ * $Id$
+ *
+ * Value_Ptr implementation based on code in Herb Sutter's book "More
+ * Exceptional C++".
+ *
+ * @author Ossama Othman <ossama@dre.vanderbilt.edu>
+ */
+//==========================================================================
+
+#ifndef ACE_VALUE_PTR_H
+#define ACE_VALUE_PTR_H
+
+#include "ace/config-lite.h"
+
+#include <algorithm>
+
+ACE_BEGIN_VERSIONED_NAMESPACE_DECL
+
+namespace ACE
+{
+ /**
+ * @struct VP_traits
+ *
+ * @brief @c Value_Ptr traits template structure.
+ *
+ * The @c Value_Ptr template class delegates some operations to this
+ * template traits structure.
+ *
+ * Specialize this trait template if cloning through copy
+ * construction is not sufficient. For example, to avoid slicing
+ * when copying an object through a base class pointer, one can
+ * implement a virtual "clone" method that can be used to
+ * polymorphically invoke the appropriate cloning operation(s).
+ * That virtual method would then be invoked by the @c VP_traits\<\>
+ * specialization.
+ */
+ template <typename T>
+ struct VP_traits
+ {
+ /// Copy the given object.
+ static T * clone (T const * p) { return new T (*p); }
+ };
+
+ /**
+ * @class Value_Ptr
+ *
+ * @brief Smart pointer implementation designed for use as a class
+ * member.
+ *
+ * Using a @c std::auto_ptr\<\> as a class member is sometimes
+ * problematic since ownership of memory is transferred when copying
+ * such members. This @c Value_Ptr class is explicitly designed to
+ * avoid such problems by performing copies of the underlying object
+ * rather than transfer ownership. This, for example, allows it to
+ * be readily used as a member in classes placed inside STL
+ * containers.
+ *
+ * @see Item 31 in "More Exceptional C++" by Herb Sutter.
+ */
+ template <typename T>
+ class Value_Ptr
+ {
+ public:
+
+ /// Constructor.
+ explicit Value_Ptr (T * p = 0) : p_ (p) { }
+
+ /// Destructor.
+ ~Value_Ptr (void) { delete this->p_; }
+
+ /// Deference operator.
+ T & operator* (void) const { return *this->p_; }
+
+ /// Pointer operator.
+ T * operator-> (void) const { return this->p_; }
+
+ /// Non-throwing swap operation used to make assignment strongly
+ /// exception-safe.
+ /**
+ * @note As implemented, the swap operation may not work correctly
+ * for @c auto_ptr\<\>s, but why would one use an @c
+ * auto_ptr\<\> as the template argument for this particular
+ * template class!?
+ */
+ void swap (Value_Ptr & other) { std::swap (this->p_, other.p_); }
+
+ /// Copy constructor.
+ Value_Ptr (Value_Ptr const & other)
+ : p_ (create_from (other.p_)) { }
+
+ /// Assignment operator.
+ Value_Ptr & operator= (Value_Ptr const & other)
+ {
+ // Strongly exception-safe.
+ Value_Ptr temp (other);
+ this->swap (temp);
+ return *this;
+ }
+
+#ifndef ACE_LACKS_MEMBER_TEMPLATES
+
+ // Compiler can't handle member templates so we lose converting
+ // copy operations.
+
+ /// Converting copy constructor.
+ template <typename U>
+ Value_Ptr (Value_Ptr<U> const & other)
+ : p_ (create_from (other.p_)) { }
+
+ /// Converting assignment operator.
+ template <typename U>
+ Value_Ptr & operator= (Value_Ptr<U> const & other)
+ {
+ // Strongly exception-safe.
+ Value_Ptr temp (other);
+ this->swap (temp);
+ return *this;
+ }
+
+#endif /* !ACE_LACKS_MEMBER_TEMPLATES */
+
+ private:
+
+#ifndef ACE_LACKS_MEMBER_TEMPLATES
+
+ /// Copying method invoked when copy constructing.
+ template <typename U>
+ T * create_from (U const * p) const
+ {
+ return p ? VP_traits<U>::clone (p) : 0;
+ }
+
+#else
+
+ // Compiler can't handle member templates so we lose converting
+ // copy operations.
+
+ /// Copying method invoked when copy constructing.
+ T * create_from (T const * p) const
+ {
+ return p ? VP_traits<T>::clone (p) : 0;
+ }
+
+#endif /* !ACE_LACKS_MEMBER_TEMPLATES */
+
+ private:
+
+#ifndef ACE_LACKS_MEMBER_TEMPLATES
+ template <typename U> friend class Value_Ptr;
+#endif /* !ACE_LACKS_MEMBER_TEMPLATES */
+
+ /// Object owned by this @c Value_Ptr.
+ T * p_;
+
+ };
+
+}
+
+ACE_END_VERSIONED_NAMESPACE_DECL
+
+#endif /* ACE_VALUE_PTR_H */