[Development] Undeprecating QString::null

Thiago Macieira thiago.macieira at intel.com
Wed Jan 17 18:18:05 CET 2018

On Tuesday, 16 January 2018 10:28:27 PST Uwe Rathmann wrote:
> On Tue, 16 Jan 2018 18:38:48 +0100, Kevin Kofler wrote:
> > So just use QString(), or define your own static instance of it if you
> > really want to microoptimize it that much.
> No it is simply that the first version of Qwt was for Qt 1.2 ( before
> QString even existed ) and during a history of almost 20 years there are
> leftovers.

Nitpick: QString existed in Qt 1.2, it just wasn't the QString we know.

It was actually the predecessor to Qt 2's QCString, which in Qt 4 became 
Q3CString and was deprecated by QByteArray.

> I had missed the point, when the static instance had been replaced -
> that's why I was erroneously concerned about BC breaks.

There's still static data, but unlike the Qt 1 solution, it's not an instance 
of QString but just of the shared null data. Since Qt 5, it's also shared with 
QVector and QByteArray. That's why the constructor is just as efficient.

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

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