On 26 Apr 07, at 6:05 AM 26 Apr 07, Arik Kfir wrote:
IMO, if the project claims to be backwards-compatible, then it should
include the older classes. If they can exist side-by-side, there
should be
no issue.
I don't think you can force every project to do this, and I think
that users would intuitively users expect that two versions of, say,
junit that are declared should show up. So what Jorg is asking for is
not unreasonable and I'm really just trying to think of the
repercussions of allowing multiple versions i.e. do we have any
plugins keying off special versions of classes: the surefire plugin
for example. I think the JMock example is perfectly valid and is
something that could be addressed in 2.1 but here is my concern and
generally why we took the strategy of not allowing this to begin with:
The classpath order is now derived from the order of the listing of
the dependencies. So in a particular project what if one case
requires class C1 from version 1.0 of JMock, and another case that
requires class C1 from version 2.0 of JMock? How are you going to
satisfy those two conditions and in general how are you going to
protect against classes that have the same name in different versions
of the JAR where both are needed?. When this case arises you are
going to need a form of paritioning, yes? Because you're going to end
up requiring features from the new version which means using the
newer classes. If you are going to need some way to say "for this
group of tests use this version of JMock" and "for this other set of
tests use that version of JMock" then you've gotten yourself into a
case that cannot be satisfied easy.
If projects could guaranteed that version N and the next major
upgrade guaranteed compatibility of the intersection of classes in
the different versions and additions were a superset of that then
adding both versions would be fine. But this is often not the case
and you get into real problems because the general rule for major
version number changes is that the API can break which means that a
class in 2.0 could be significantly different in API and structure
then its equivalent in 1.0.
In Ant you might create a separate classpath with different JARs and
apply that to a different set of classes. We avoid this by simply
saying, this is just too complicated and take your tests, create
another module that uses the new version of JMock and be done with it.
What is easier: creating a separate module which has this simple rule
of allowing only one version of a dependency and using all the same
patterns of every other type of Maven module. Or allow multiple
versions and then start trying to rig up ways to defend against
incompatibilities and partitioning sets of classes for use with a
particular dependency? I think just making another module is easier.
Are you sure you can defend against and cope with the two versions of
JMock without any problem? Nat is a bright guy, and is probably very
careful about changes between versions but lots of project are not
and we decided not to allow multiple versions to protect people from
less then stringent practices that generally happen in real life.
We tried to make the rules for a single module simple, and make it
simple to create new one. It's just so much easier for the rest of
the tool chain to understand then trying to deal with the innumerable
variations that occurs when multiple anything is allowed: multiple
versions, multiple source trees, and multiple artifacts per unit of
work which is a POM/module in Maven.
That's the not so short answer, but the reason why we do what we do.
I know what users expect to happen, but try to think of the counter
examples where things might go wrong by using multiple versions in
the same module.
Jason.
I see your point, though - I just don't think it is methodology-
correct to
use different versions of the same project in one place, regardless
of the
saying that "it works", because it just doesn't seem "right" to me...
anyway - just my 2 cents; I have no real objection for Maven to
support
declaring two dependencies of the same artifact with different
version.
cheers,
Arik.
On 4/26/07, Jörg Schaible <[EMAIL PROTECTED]> wrote:
Grzegorz Slowikowski wrote on Thursday, April 26, 2007 10:47 AM:
> Hi
>
> Look at hibernate2 and hibernate3 artifacts. They have
"hibernate" and
> "org.hibernate"
> groupIds respectively, so they can be used together (java package
> names are different too).
> This is IMO the proper way to do this.
>
> While writing this mail I found:
> http://jira.codehaus.org/browse/MAVENUPLOAD-1500#action_94054
>
> which confirms what I have written above.
You simply acknowledge that the problem exists! The fact that
jMock will
now switch groupId form jmock to org.jmock is exactly driven by this
limitation. The first question I received from Nat of jMock was:
"And what
will happoen next time?". And I would rather think about the
consequences
regarding M2.1 now instead of putting my head into the sand.
- Jörg
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