Hi Marc,
On 05/12/2015 19:06, Marc Mutz wrote:
On Saturday 05 December 2015 13:00:44 Sean Harmer wrote:
So given the above example we'd be able to have something like this
(name of macro pending):
if (e->type() == NodeUpdated) {
const QScenePropertyChangePtr &propertyChange =
qSharedPointerCast<QScenePropertyChange>(e);
switch (propertyChange->propertyNameStringId()) {
case qStrId("scale3D"):
m_scale = propertyChange->value().value<QVector3D>();
updateMatrix();
break;
case qStrId("rotation"):
m_rotation = propertyChange->value().value<QQuaternion>();
updateMatrix();
break;
case qStrId("translation"):
m_translation = propertyChange->value().value<QVector3D>();
updateMatrix();
break;
case qStrId("enabled"):
m_enabled = propertyChange->value().toBool();
break;
default:
qWarning() << "Unknown property update";
}
}
Where the qStrId macro expands to nothing and the preprocess tool
replaces its contents with the hashed value. No idea if all of our
supported compilers allow hooking in custom preprocessors or not.
How do you handle the invariable hash collisions?
Not sure yet. Still thinking this through.
The chances of a collision within the scope of a comparison such as this
is pretty small (of course dependent upon the quality of the hash
function). If used within a hash the compiler would complain about
duplicated case labels.
If the preprocess tool maintains a catalogue of entries in the hash it
could also warn about collisions to allow the user opportunity to alter
the names being used.
What's wrong the the old and trusted
switch (propName.front()) {
case 's': if (propName == "scale3D") ...
case 'r': if (propName == "rotation") ...
Indeed, this is something we could adopt now with little effort. I was
just wondering if we could get it down to the theoretical ideal of a
single integer comparison mapped into the finite set of strings in use.
Seems not, without some non-neglible effort.
(and why the QByteArrayLiteral in the original code)?
Simple oversight. Will fix.
Cheers,
Sean
--
Dr Sean Harmer | [email protected] | Managing Director UK
KDAB (UK) Ltd, a KDAB Group company
Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090
Mobile: +44 (0)7545 140604
KDAB - Qt Experts
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