Hi Nikos & Scott, IMO, both of you are right, but you are discussing two different things.
Debao On Thu, Apr 26, 2012 at 4:13 PM, Nikos Chantziaras <rea...@gmail.com> wrote: > On 27/04/12 01:48, Scott Aron Bloom wrote: >> I'm not sure if you're serious or are trolling me for fun. I *do* have >> a sense of humor, but this one I don't get :-/ >> >> How is this "wrong?" You claim that if you do: >> >> QList<int> someOtherList; >> QList< QList<int> > list; >> list.append(someOtherList); >> >> you are able to modify 'someOtherList' through 'list'. You just can't. >> Not the list, and also not its contents (since they're 'int', not >> 'int*'). If you really are serious about what you're saying, even after >> this discussion, then I have to give up. >> ---------------- >> It has NOTHING TO DO WITH THE int vs int*, > > I only mentioned it in passing. > > >> It has EVERYTHING to do with >> you are sending in a const copy of the someOtherList... > > Actually that's also wrong. You are not sending a const copy. You are > sending a const reference. But it doesn't matter. That's just an > implementation detail done for optimization reasons. You cannot modify > it and it has to be treated as a copy. > > >>> If the container list, allowed for non-const parameters passing (like >>> it could in Qt 3.0) You COULD "copy" the original and modify it. >> >> Isn't that the point? That you CANNOT modify it through the copy, >> therefore if you do need to modify it you need a pointer rather than a >> copy? But at the same time you claim the opposite. >> >> Or this is some kind of miscommunication. >> -------------------------- >> >> I claim, that with implicit sharing YOU CAN MODIFY the original list... >> however, not via the constant.. Try using the operator[] instead. > > I already did and demonstrated that the original does not get modified: > > listOfInts.append(10); > listOfLists.append(listOfInts); > listOfLists[0][0] = 9; > qDebug() << listOfLists[0][0] << listOfInts[0]; > > Using listOfLists[0][0] to modify listOfInts does NOT work. Why don't > you try the above yourself? > > >>> But keeping a pointer to something on the stack, that could go out of >>> scope, is VERY VERY dangerous... >> >> No one claimed otherwise. >> ---------------- >> >> You did when you suggested you use >> >> push(&otherList ) > > I did not "suggest" this. This was listed, inside a comment, as an > example. No one can suggest anything, because the OP did not state what > it is he wanted to put in the list. So I wrote: > > list->append(new QList<int>); > // Or: > // list->append(&someOtherList); > > I am not teaching basic C++ whenever I post a solution to a problem :-/ > I assume that everybody knows that variables not created on the heap > get destroyed when they go out of scope. > > >> You are coming to the correct conclusing, but not for the correct >> reason.. Using append/pushback etc, the list is copied using a const >> reference to the data.. > > Again, it is not copied, a const reference is held. But it doesn't matter. > > >> Implicit sharing or not, will not allow modifications on either the copy >> or the original to propagate to the other > > Then what exactly is the issue here? You end up agreeing with me, but > there seems to be still some kind of issue? > > _______________________________________________ > Interest mailing list > Interest@qt-project.org > http://lists.qt-project.org/mailman/listinfo/interest _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
