Use-cases for version ranges?

[Neil Bartlett]

I noticed that I failed to address your point about Maven using point versions.

Maven is a build tool. At build time we need to compile against a
single specific version so that we have repeatable builds. In general
we should build each module against the lowest version of the library
that it can possibly use, and there are no major negative consequences
of having several versions of a library at build time (except that
Maven has to download a lot!). At runtime however we need to have the
flexibility to substitute a single compatible version.

Neil

On Fri, Nov 18, 2011 at 7:10 AM, Neil Bartlett <njbartlett at gmail.com> wrote:
> Suppose as the developer of module A, I declare a dependency on log4j,
> exactly version 1.0.0 because I have not tested against log4j 1.0.1,
> 1.0.2, 1.3, 999.999 etc. I effectively prevent my module *ever* being
> used with log4j version 1.0.1 even if this combinations is later
> tested and proven to work by somebody else. In other words, testing is
> important but it doesn't necessarily have to always be done by the
> original developer of each module.
>
> On the other hand let's say I state my dependency using the following
> range: [1.2.14, 2.0). This is OSGi syntax and I believe Jigsaw is
> following it, and it simply means I accept version 1.2.14 up to but
> not including 2.0. Anybody can see that I compiled and tested against
> 1.2.14, but has the option of using 1.2.15, 1.2.16, 1.3, 1.9 etc. It
> does not mean that I *guarantee* my module will work with log4j 1.3
> because that obviously depends on whether the log4j authors accept and
> follow the common semantics of indicating backwards-incompatible
> changes with a bump to the first version segment.
>
> The consequence of trying to lock down imports to a narrow range or
> even a point version is that assembling an application becomes very
> difficult, and we are forced to deploy many versions of common
> libraries concurrently. This is non-optimal, though we can handle it
> to some degree via per-module classloaders as in OSGi.
>
> Regards,
> Neil
>
> On Thu, Nov 17, 2011 at 11:52 PM, cowwoc <cowwoc at bbs.darktech.org> wrote:
>> Can someone please explain why modules need to be able to specify version
>> ranges for dependencies? I believe OSGI allows the specification of version
>> ranges while Maven allows the specification of individual versions.
>>
>> The only thing that comes to mind is when module C depends on A and B, A
>> depends on log4j 1.0, and B depends on log4j 1.1. What does C do? Is this
>> the main use-case for version ranges?
>>
>> By the sound of it, this is a trust model where developers are told that
>> log4j 1.x won't break compatibility so they depend on that range without
>> actually testing against each version (newer versions may be released after
>> their own software). I question whether such a mechanism is better or worse
>> than depending on individual versions which may be overridden at a later
>> time (a la Maven). On the one hand, you don't need to release a new version
>> of the application each time a dependency is updated. On the other hand, no
>> one is actually running tests to ensure that the versions are really
>> compatible.
>>
>> Is there a way to get module A to see log4j 1.0 and module B to see log4j
>> 1.1 (using separate ClassLoaders)?
>>
>> Thanks,
>> Gili
>>
>> --
>> View this message in context: http://jigsaw-dev.1059479.n5.nabble.com/Use-cases-for-version-ranges-tp5002801p5002801.html
>> Sent from the jigsaw-dev mailing list archive at Nabble.com.
>>
>