With this and QPROPERTY you can use portSpeeds() and portSpeeds.

We don't have extruderCountChanged signal.

I think you only get to have one either the function is part of a property or its invokable.

Not required to have a write since this is a const

according to http://doc.qt.io/qt-5/properties.html

The only required item for a QPROPERTY is READ.
I suggest we also look to adding CONSTANT to varibles where it makes sence.

The presence of the CONSTANT attibute indicates that the property value is constant. For a given object instance, the READ method of a constant property must return the same value every time it is called. This constant value may be different for different instances of the object. A constant property cannot have a WRITE method or a NOTIFY signal

^describes portSpeed perfectly .

unless there's a signal that will send the current port. if the value is *static* it doesn't matter.

if you change the printer, does the exturderCount *can* change?
if so, this is wrong.

Yes the extruder count is updated on connect to a printer. So if you connect to a printer with a different number of extruders it should change.