Fix crash on recursive include (bug #8994)

[lyx.git] / src / support / copied_ptr.h

diff --git a/src/support/copied_ptr.h b/src/support/copied_ptr.h
index 0683158d811a35b3934b2e4c9a3255446b2a5d85..15ef7551e3be0356e273b093941c7690b9df815c 100644 (file)
--- a/src/support/copied_ptr.h
+++ b/src/support/copied_ptr.h
@@ -4,15 +4,21 @@
  * This file is part of LyX, the document processor.
  * Licence details can be found in the file COPYING.
  *
- * \author Yonat Sharon http://ootips.org/yonat/
+ * \author Angus Leeming
  *
- * simple copy-on-create/assign pointer.
+ * A templated class that can serve as a pointer to an object, with the
+ * property that when the copied_ptr is copied, it creates its own copy
+ * of the object pointed to as well.
  *
- * Note: If the actual object pointed to belongs to a derived class,
- * then copied_ptr will not create a copy of the derived class object,
- * but a new base class object.
- * If you want to use a polymorphic copy-on-assign pointer, use
- * cloned_ptr.
+ * The implementation was based originally on Yonat Sharon's copied_ptr templated
+ * class, as described at http://ootips.org/yonat/, but has evolved toward's
+ * Herb Sutter's HolderPtr, as described at http://www.gotw.ca/gotw/062.htm.
+ * (Note, HolderPtr became ValuePtr in his book, More Exceptional C++.)
+ *
+ * Warning: if the class stores 'Base * ptr_', but the actual object pointed to
+ * belongs to a derived class, then you must specialise memory_traits<Base> so that
+ * its clone and destroy member functions do the right thing. Otherwise, you'll
+ * end up slicing the data.
  */
 
 #ifndef COPIED_PTR_H
@@ -22,11 +28,18 @@ namespace lyx {
 namespace support {
 
 template <typename T>
+struct memory_traits {
+       static T * clone(T const * ptr) { return new T(*ptr); }
+       static void destroy(T * ptr) { delete ptr; }
+};
+
+
+template <typename T, typename Traits=memory_traits<T> >
 class copied_ptr {
 public:
        explicit copied_ptr(T * = 0);
-       ~copied_ptr();
        copied_ptr(copied_ptr const &);
+       ~copied_ptr();
        copied_ptr & operator=(copied_ptr const &);
 
        T & operator*() const;
@@ -35,68 +48,59 @@ public:
 
 private:
        T * ptr_;
-       void copy(copied_ptr const &);
 };
 
 
-template <typename T>
-copied_ptr<T>::copied_ptr(T * p)
+template <typename T, typename Traits>
+copied_ptr<T, Traits>::copied_ptr(T * p)
        : ptr_(p)
 {}
 
 
-template <typename T>
-copied_ptr<T>::~copied_ptr()
-{
-       delete ptr_;
-}
+template <typename T, typename Traits>
+copied_ptr<T, Traits>::copied_ptr(copied_ptr const & other)
+       : ptr_(other.ptr_ ? Traits::clone(other.ptr_) : 0)
+{}
 
 
-template <typename T>
-copied_ptr<T>::copied_ptr(copied_ptr const & other)
+template <typename T, typename Traits>
+copied_ptr<T, Traits>::~copied_ptr()
 {
-       copy(other.get());
+       Traits::destroy(ptr_);
 }
 
 
-template <typename T>
-copied_ptr<T> & copied_ptr<T>::operator=(copied_ptr const & other)
+template <typename T, typename Traits>
+copied_ptr<T, Traits> & copied_ptr<T, Traits>::operator=(copied_ptr const & other)
 {
-        if (&other != this) {
-               delete ptr_;
-               copy(other);
-        }
-        return *this;
+       if (&other != this) {
+               copied_ptr temp(other);
+               std::swap(ptr_, temp.ptr_);
+       }
+       return *this;
 }
 
 
-template <typename T>
-T & copied_ptr<T>::operator*() const
+template <typename T, typename Traits>
+T & copied_ptr<T, Traits>::operator*() const
 {
        return *ptr_;
 }
 
 
-template <typename T>
-T * copied_ptr<T>::operator->() const
+template <typename T, typename Traits>
+T * copied_ptr<T, Traits>::operator->() const
 {
        return ptr_;
 }
 
 
-template <typename T>
-T * copied_ptr<T>::get() const
+template <typename T, typename Traits>
+T * copied_ptr<T, Traits>::get() const
 {
        return ptr_;
 }
 
-
-template <typename T>
-void copied_ptr<T>::copy(copied_ptr const & other)
-{
-       ptr_ = other.ptr_ ? new T(*other.ptr_) : 0;
-}
-
 } // namespace support
 } // namespace lyx