Use-cases for version ranges?

[Neil Bartlett]

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
>
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