On 24/03/2021 13:49, Matthew Woehlke wrote:
Let's take e.g. QList::toSet as an example. The deprecation message says to use `QSet(list.begin(), list.end())` instead. How, then, is the correct implementation*not*:QSet<T> QList<T>::toSet() { return QSet<T>{begin(), end()}; }
That is the correct implementation, but the deprecation functions aren't about "how this ought to be implemented into Qt".
What was so hard about that? If that's wrong, then so AFAICT is the deprecation message.
Probably. There's only so much space for the message in them. I'm trying to point out that the specific motivation here isn't even remotely _technical_ (e.g. is this hard to implement correctly; as you've shown, it's super easy), but a _design_ one (is this API *good*?).
And anyways these methods are still fully supported within Qt 5.
Yes, it does not generalize to every possible container type, but I don't know that anyone is asking for that (and I agree we shouldn't tryto support that).
All the contrary, this is one big crux of the problem: toX() for a completely arbitrary closed set of X is bad API. Why QSet::toList and not toVector? Why QList::toSet and not, say, MULTI sets? If you want stability of references and can't use Q6Set but want std::unordered_set, why there isn't a function for that? And so on.
This is calling for a more generic toX() API. Which isn't easy to provide within the quality constraints of QtCore. If it were, don't you think Yours Truly would already have provided it? Do I sound *that* evil that I enjoy crippling for the sake of it? :-(
We're not talking about adding many, many variations
upon this theme, just*not* removing the ones that already existed. The ones that do exist, exist because they are more convenient to use, and because they cover*the most common* use cases.
Can I hear some use cases then please? Because from the experience of usages within Qt, it was a nail/hammer problem, call it an education problem ("I know containers; I don't know algorithms; let me use containers to solve an algorithmic problem"), of which we're entirely responsible (Qt docs teach a lot about containers, but not about algorithmic design.)
Miscellanea examples from Qt itself, * I need to remove duplicates from my list, let me do:
list = list.toSet().toList();
* I need to keep the list, process it in order, but avoid processing duplicate elements; 99% of the time the list is a handful of elements; let me do
QSet s; for (elem : list) { if (!s.contains(elem)) { s.insert(elem);
process(elem); } }
And so on. -- Giuseppe D'Angelo | giuseppe.dang...@kdab.com | Senior Software Engineer KDAB (France) S.A.S., a KDAB Group company Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com KDAB - The Qt, C++ and OpenGL Experts
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