[Development] Qt6: Adding UTF-8 storage support to QString

[Thiago Macieira]

On Friday, 18 January 2019 08:13:40 PST Kai Koehne wrote:
> 1. We generally compile Qt code with QT_NO_CAST_FROM_ASCII that disables the
> QString(const char *) overload. And we do that so that you have to make it
> explicit whether you really want to do the implicit conversion from UTF-8
> to UTF-16, use QStringLiteral() to encode it as UTF-16 at compile time, or
> rather have it translated with a  tr() call.
> 
> I think for Qt code explicit is better than implicit, so I actually would
> stay with QT_NO_CAST_FROM_ASCII.

Actually, what we should do is allow everywhere

	functionTakingString(u"Tor Arne Vestbø")
	// (note the u)

Which causes the compiler to encode the string in UTF-16, bypassing the need 
for runtime decoding, and enforcing sources as UTF-8, so we get consistent 
binaries. It's just one step short of QStringLiteral in that it will still 
allocate memory, but it only needs a memcpy. Such code also works with 
functions taking QStringView without memory allocation.

We all know that QStringLiteral has drawbacks when it comes to unloading 
modules. For QtCore, obviously QStringLiteral is not a problem, but other 
modules may decide to avoid it.

PS: I still want to improve QStringLiteral, but it will still be different 
from a pure char16_t literal.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center