Define and use utility template ValueIterator...

... generalizing the fix of commit 7591891 to other cases, making the iterators
safe for adaptation with std::reverse_iterator should the need ever arise

src/MemoryX.h

@@ -430,6 +430,19 @@ template< typename T >
 ValueRestorer< T > valueRestorer( T& var, const T& newValue )
 { return ValueRestorer< T >{ var, newValue }; }
 
+/**
+  \brief A convenience for defining iterators that return rvalue types, so that
+  they cooperate correctly with stl algorithms and std::reverse_iterator
+ */
+template< typename Value, typename Category = std::forward_iterator_tag >
+using ValueIterator = std::iterator<
+   Category, const Value, ptrdiff_t,
+   // void pointer type so that operator -> is disabled
+   void,
+   // make "reference type" really the same as the value type
+   const Value
+>;
+
 /**
   \brief A convenience for use with range-for
  */

src/Track.h

@@ -834,16 +834,7 @@ template < typename TrackType > struct TrackIterRange;
 template <
    typename TrackType // Track or a subclass, maybe const-qualified
 > class TrackIter
-   : public std::iterator<
-      std::bidirectional_iterator_tag,
-      TrackType *const,
-      ptrdiff_t,
-      // pointer is void to disable operator -> in the reverse_iterator...
-      void,
-      // ... because what operator * returns is really a value type,
-      // so you can't take its address
-      TrackType *const
-   >
+   : public ValueIterator< TrackType *, std::bidirectional_iterator_tag >
 {
 public:
    // Type of predicate taking pointer to const TrackType

src/WaveTrack.h

@@ -378,7 +378,7 @@ private:
    // Get access to all clips (in some unspecified sequence),
    // including those hidden in cutlines.
    class AllClipsIterator
-      : public std::iterator< std::forward_iterator_tag, WaveClip* >
+      : public ValueIterator< WaveClip * >
    {
    public:
       // Constructs an "end" iterator

src/toolbars/ToolDock.h

@@ -114,7 +114,7 @@ public:
    // This iterator visits the nodes of the forest in pre-order, and at each
    // stop, reports its Place
    class Iterator
-      : public std::iterator<std::forward_iterator_tag, Place>
+      : public ValueIterator<Place>
    {
    public:
       const Place &operator * () const { return mPlace; }