On 2019-07-10 14:55, André Pönitz wrote:
On Wed, Jul 10, 2019 at 11:29:15AM +0200, Mutz, Marc via Development
wrote:
On 2019-07-10 10:50, Arnaud Clere wrote:
> Hi all,
>
> So, do I understand correctly that:
> 1. QUtf8String may be required in Qt7 to solve problems due to C++2x
> char8_t
I wouldn't say required. I also don't think it needs to wait until Qt
7. Qt
7 is where we may depend on C++20 and can use char8_t in the interface
and
implementation, but we should certainly not wait for that to add the
class.
It's certainly a good idea, IMO, to have views and owning containers
that
operate on L1, UTF-8 and UTF-16 strings. The views are more important.
> 2. QByteArray methods currently operating on latin1 may be restricted
> to ascii in Qt6 to avoid problems when const char* input really is
> utf8
I have no opinion on that.
> 3. QLatin1String may become QLatin1StringView by Qt7
Qt 6. We can add the name as an alias now, make QLatin1String an
owning
container for Qt 6.0 (it breaks no code, just makes it slower, and the
port
is trivial), and QLatin1StringView becomes what QLatin1String is now.
As far as I understand there's a perceived need to have "full" utf8
literals, and there's a need to have ASCII literals. First could be
served by some QUtf8*, second by QAscii*, both additions, no need to
change QLatin* semantics.
L1 is special because it's the first plane of Unicode, so conversion
between the two will always be faster than between other encodings. This
is why it makes sense to use all 8 bits and have L1, not artificially
restrict to US-ASCII strings. That's one reason: opportunism.
The other reason is about error checking: What should the result be of
putting an æ into a QAsciiString? Assert at runtime? UB? In
QLatin1String, this error just can't happen. Even if you feed it UTF-8,
you may get mojibake, because you picked the wrong encoding, but it's
not an error. Any UTF-8 octet sequence is a valid L1 string.
So, I don't see QAscii* pulling it's weight.
Thanks,
Marc
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