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?
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