[Kstars-devel] Porting to Qt4: avoid pointers in QLists?

[Jason Harris]

Hello,

I am starting to work on porting the code to Qt4.  It's going to be a pretty 
big job, because we make very heavy use of classes that no longer exist.  
Before I really start ripping things apart, I thought it would be useful to 
discuss some potential guidelines.

For this thread, let's concentrate on the QPtrList -> QList move.  This is 
going to be the biggest chore; we use QPtrList just about everywhere.
  
From the Qt4 porting guide 
(http://doc.trolltech.com/4.0/porting4.html#qptrlist-t), we learn that the 
equivalent of this old code:

  QPtrList<SkyObject> objList;
  //assume the list gets populated somehow...
  for ( SkyObject *o = objList.first(); o; o = objList.next() ) {
    //do stuff to o
  }

is now:

  QList<SkyObject*> objList;
  //assume the list gets populated somehow...
  for ( int i=0; i < objList.size(); ++i ) {
    SkyObject *o = objList[i];
    //do stuff to o
  }

(note: there is also a QLinkedList class, if an iterator-type accessor is 
somehow preferred to the [] random-access operator...)

However, there is no auto-delete for QList items.  So, we would need to do 
this at some point to avoid memory leaks:

  while ( ! objList.isEmpty() ) delete objList.takeFirst();


Another option I want to consider is to simply avoid pointers as QList 
members.  Then we don't need to worry about deleting list members.  I don't 
think performance will be impacted; QList still uses pointers internally, and 
the trolls claim that QList access is very fast.  In fact, the docs for QList 
claim that QList is usually faster than QVector, even though QVector 
guarantees that the items are stored at adjecent locations in memory.

Does anyone have objections to adopting a guideline that QLists should not 
have pointer members?  Is there a downside that I am missing?

thanks,
Jason
-- 
KStars: KDE Planetarium
http://edu.kde.org/kstars