[Kst] branches/work/kst/kst1kde4/kst/src/libkst

Peter Kümmel syntheticpp at gmx.net
Fri Nov 20 19:14:21 CET 2009

What about splitting out the update functionality in a new class,
eg. 'Updatable'?


Barth Netterfield wrote:
> Actually, I am in the midst of a major update system redesign.
> Kst::Object provides the interface for a number of general things related to 
> updates.
> cbn
> On Friday 20 November 2009 12:20:52 Peter Kümmel wrote:
>> Now I realize, sharedptr.h is only to implement a thread save smart
>>  pointer, with the disadvantage that a class which SharedPtr points to must
>>  inherit from Shared. So sharedptr.h could be completely replaced by
>>  QSharedPointer.
>> I also have the impression often the only feature used from Object is the
>> memory management, so I wonder if we couldn't remove inheritance of Object
>> at several classes, because QSharedPointer works with any class.
>> Peter
>> Barth Netterfield wrote:
>>> http://labs.trolltech.com/blogs/2009/08/25/count-with-me-how-many-smart-
>>> pointer-classes-does-qt-have/
>>> I *think* we are OK with QSharedPointer for Kst::Object as long as we
>>> make sure that every Kst::Object that gets created is only pointed to by
>>> a QSharedPointer (and never a normal pointer). And this is good policy
>>> anyway.
>>> In this case, we would never call delete on a Kst::Object -
>>> QSharedPointer takes care of that for us.
>>> The QExplicitlySharedPtr class is used for sharing data, not pointers.  I
>>> don't see any use case for copy-on-write for Kst::Object (in fact, copy
>>> contstuctors aren't even defined).  So in principle, they would work -
>>> but I think at this point we will be much happier with QSharedPointers,
>>> as long as we follow the simple rule: No Kst::Object *s anywhere!
>>> This won't work for Kst::ViewItem, unfortunately, since these are all
>>> held by the QGraphicsItem class as plain pointers... so, no smart
>>> pointers for Kst::ViewItems at this point.
>>> cbn
>>> On Thursday 19 November 2009 12:49:12 Peter Kümmel wrote:
>>>> Barth Netterfield wrote:
>>>>> On November 19, 2009 11:43:27 am Peter Kümmel wrote:
>>>>>> do we need the 'Explicitly' version?
>>>>> Explicitly shared objects inherit from a class which keeps track of
>>>>> their usage counts internally.  With QShared, the pointer itself keeps
>>>>> tack of usage - which is harder to manage.
>>>>> cbn
>>>> I know the Qt's classes where QSharedData is used to implement
>>>> shared data classes.
>>>> Implicit or "copy on write" classes, like most of Qt's classes, use
>>>> QSharedDataPointer internally, classes which do not support "copy
>>>> on write" and
>>>> where you have to detach manually (explicit) uses
>>>> QExplicitlySharedDataPointer internally:
>>>> http://doc.qt.nokia.com/4.6-snapshot/qshareddata.html
>>>> For reference counting there is QSharedPointer.
>>>> We should map kst's classes to Qt's classes, and therefore the
>>>> question:
>>>> Do we need shared data objects where we have to call detach() or
>>>> is "copy on write"
>>>> enough. "copy on write" is less error prone because you could not
>>>> forget to call
>>>> detach.
>>>> Peter
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