Really? Nokia is updating Qt 4.7.4 phones like 701 or N8 to Qt 4.8 with Belle. Should be possible on the N9 too I think.
Qt minor releases (4.0 -> 4.8) are all binary compatible. Meaning an application built against 4.0 will be runnable against 4.8. Note that this doesn't go backwards.
Major releases (3 -> 4, 4 -> 5) are not binary compatible. At the very least, they need a rebuild - but major releases also usually break API in some forms. 4 -> 5 is a fairly minor case of that though, so stuff mostly will just work with a rebuild.
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Also interested in this - Qt 5 (5.1+) is one of the two main pre-requsites for running the new QtQuick 2.0 based modRana graphical interface. The second on is Python 3.2+. Once both are available PyOtherSide can be built and the interface should run.
As for how it looks like and what it can do, check the Sailfish OS modRana package, which is using the QtQuick 2.0 interface by default.
__________________ modRana: a flexible GPS navigation system Mieru: a flexible manga and comic book reader Universal Components - a solution for native looking yet component set independent QML appliactions (QtQuick Controls 2 & Silica supported as backends)
Major releases (3 -> 4, 4 -> 5) are not binary compatible. At the very least, they need a rebuild - but major releases also usually break API in some forms. 4 -> 5 is a fairly minor case of that though, so stuff mostly will just work with a rebuild.
i'm a Qt expert and former Jolla sailor (forever sailing, in spirit).
if you like, read more about me.
if you find me entertaining, or useful, thank me. if you don't, then tell me why.