[Development] RFC: Proposal for a semi-radical change in Qt APIs taking strings

[Konstantin Ritt]

If QString in Qt6 could be { QArrayData *d; ushort *b; int s }, then it
supersedes QStringView in all aspects:
- QString(u"hello world", 5) /* { d=.., b=.., s=5 } */ - still has a
superpower of COW, etc
- QString::fromRawData(u"hello world", 5) /* { d=nullptr, b=.., s=5 } */ -
explicitly means "no owning, deep-copy when necessary"

then we could get rid of QStringRef (or typedef it to QString) and do
something like:

private:
QString(QArrayData *dd, ushort *unicode, int size) { if (dd) { dd->ref(); }
d = dd; b = unicode; s = size; } /* not that trivial, of course, just to
describe the idea */
public:
QString QString::left(int n) const { return QString(d, b, n); }
QString QString::leftRef(int n) const { return QString(nullptr, b, n); }


> That said, QStringView is as much about
>
> - slim interface type vs. thick, fat, storage type
> - interop with 3rd-party and native code

So as QString now... i.e.

DWORD dwBufferSize = 0;
if (::GetUserProfileDirectory(token, NULL, &dwBufferSize) == 0 &&
dwBufferSize != 0) {
    QVarLengthArray<wchar_t> userDirectory(dwBufferSize);
    if (::GetUserProfileDirectory(token, userDirectory.data(),
&dwBufferSize) == 0) {
        QString dirName = QString::fromRawData(userDirectory.constData(),
dwBufferSize); // still unsafe, but it is clearly documented for years and
nothing has really changed for its users anyways
        return QDir().exists(
dirName.rightRef(dirName.lastIndexOf(QLatin1Char('\\'))));
    }
}


Regards,
Konstantin
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