[Development] binary compatibility promise

[Ziller Eike]

On 23 Nov 2012, at 11:20, Peter Hartmann <phartmann at rim.com> wrote:

> On 11/23/2012 11:11 AM, Poenitz Andre wrote:
>> Peter Hartmann wrote:
>>> On 11/23/2012 12:12 AM, André Pönitz wrote:
>>>> (...)
>>>> The reality is that this guarantee often enough does not hold in
>>>> practice. Vendors of "binary" Qt based application typically test their
>>>> setup against one specific (often enough patched) version of Qt which
>>>> is then shipped with the application. Users are not expected to switch
>>>> Qt versions, except when upgrading the whole application. Insofar are
>>>> rules like "we can't add symbols in patch releases" not much more then
>>>> self-inflicted pain without measurable gain.
>>> 
>>> This situation is different on mobile (and I guess embedded as well);
>>> for BlackBerry10 we have one version of Qt on the device
>> 
>> Do you intend to upgrade this version of Qt that's installed on the device
>> without upgrading the applications using it?
> 
> yes, e.g. device updates and 3rd party apps in the store.

Well, even for device updates & 3rd party apps, the most sensible thing IMO is to provide a "beta period" for the device update to 3rd party app developers, so they can test their applications against the new versions and possibly update their application in the store.
I mean there *are* behavior changes in every new version of Qt, also patch releases, that's what "bugfixing" is about ;). That might affect one or the other application in a negative way, in addition to the one or other bug that unfortunately gets introduced.

Regarding "can you run an application that was compiled against x.y.z also with x.y.(z-1)", I think that is simply a question of defining a policy. Also for shared Qt versions on devices, it is just a policy against which Qt version applications should be compiled to run on the wanted number of device installations.

-- 
Eike Ziller, Senior Software Engineer - Digia, Qt
 
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