Stanley Ho's Blog

Versioning in the Java Module System (Part 2)

Version ranges

First, the Java Module System (in the forthcoming JSR 277 EDR2) adopts the OSGi syntax for version range intervals. [ and ] mean the bound is inclusive and ( and ) mean the bound is exclusive:

    [1.2.3, 4.5.6)    ~ 1.2.3 <= x < 4.5.6
    (1.2.3, 4.5.6]    ~ 1.2.3 < x <= 4.5.6
    (1.2.3, 4.5.6)    ~ 1.2.3 < x < 4.5.6
    [1.2.3, 4.5.6]    ~ 1.2.3 <= x <= 4.5.6

Where the Java Module System differs from OSGi is in the interpretation of a single version. OSGi interprets a single version like 1.2.3 as "1.2.3 or greater" (OSGi R4.1 3.2.5). To get precisely version 1.2.3, you must write [1.2.3,1.2.3]. Adopting an implicit range is certainly concise, and use of exact versions is sufficiently rare that their [...,...] overhead is not too bad. But millions of programmers will first encounter versions via the Java Module System and it is best to adopt the simplest possible interpretation of any term. There is no doubt that someone seeing 1.2.3 for the first time thinks "exactly 1.2.3", so that is how the Java Module System interprets it. Ranges are denoted with explicit symbols. '+' means "or greater":

    1+        ~ [1, infinity)       ~ 1 <= x < infinity
    1.2+      ~ [1.2, infinity)     ~ 1.2 <= x < infinity
    1.2.3+    ~ [1.2.3, infinity)   ~ 1.2.3 <= x < infinity
    1.2.3.4+  ~ [1.2.3.4, infinity) ~ 1.2.3.4 <= x < infinity

    1.*      ~ [1, 2)            ~ 1 <= x < 2
    1.2.*    ~ [1.2, 1.3)        ~ 1.2 <= x < 1.3
    1.2.3.*  ~ [1.2.3, 1.2.4)    ~ 1.2.3 <= x < 1.2.4

The Java Module System also allows groups of ranges to be expressed, separated by ';'. These "union ranges" are separated by ';' because it works in command line expressions, unlike ',' and '&' !

    1.* ; [2.0, 2.7.3)                ~ 1.0.0 <= x < 2.7.3
    [1.2.3.4, 2.0) ; 2.* ; 3+         ~ 1.2.3.4 <= x < infinity

   [1, 3) - 2.5.*

   [1, 2.5)   ; [2.6, 3)

   [1, 2.4.*] ; [2.6, 3)

   [1, 3) - 2.5.1.*

   [1, 2.5.1)   ; [2.5.2, 3)

   [1, 2.5.0.*] ; [2.5.2, 3)

The cardinality of the exclusion does affect the length of the union, so excluding two version ranges:

   [1, 3) - 2.5.1.* - 2.6.8.*

   [1, 2.5.1)   ; [2.5.2, 2.6.8)   ; [2.6.9, 3)

   [1, 2.5.0.*] ; [2.5.2, 2.6.7.*] ; [2.6.9, 3)

In summary, we think it is reasonable for the Java Module System to let version numbers be version numbers, and introduce simple syntax (+, *) to denote ranges. Intervals work as they do in OSGi. Complex scenarios can use ; to group ranges and intervals.

Comments

• Stanley, did you consider allowing other qualifiers to the dependencies. Like "tested on", "should work with", "definitely won't work with", or even "has better performance with" qualifiers. That would allow for optimizing the dependencies based on the preferences by the user.

  Posted by: r_spilker on May 30, 2008 at 05:25 AM

• I think it's a huge mistake to make depending on a single exact version to be the easiest thing to do. If your code really does work *only* with version 1.2.3, and neither 1.2.2 nor 1.2.4 will do, then it's quite right that OSGi makes you jump through a minor hoop to be explicit about that fact.
  Developers are lazy. If single version dependencies are the default then we will get a whole pile of libraries that have single version dependencies. Imagine the mess that will result. "What's that, you have version 1.2.15 of Log4J? Sorry, I only work with version 1.2.14. You'll just have to install both versions and partition your class space." Probably no application will work without multiple versions of every library it uses.
  Sure, the assumption that "x" means "x or above" is not perfect because sometimes a module will bind to a library version it can't handle. But defaults never can be perfect... the key is to choose the default that causes least harm.

  Posted by: njbartlett on May 30, 2008 at 03:16 PM

• I have to say I like the +,*. It is clearly more intuitive without a lot of extra effort.

  Posted by: lstroud on May 31, 2008 at 06:18 AM

• This JSR is turning into a philosophy class!! ... a debate of minutia. So much thought is going on to reinventing the wheel (i.e., versioning), and all the development is going on in private. Stanley, I don't think the public will give you a break until it appears the work is less secretive and less esoteric. And please, stop comparing against OSGi to show how this JSR uses so-called better conventions. Replicate what works.

  Posted by: paulusbenedictus on June 01, 2008 at 06:34 AM

• The range syntax looks decent to me but I agree with paulusbenedictus that this discussion should be opened to the public using a discussion forum or something. The blog commenting system is not made for this sort of thing.

  Posted by: cowwoc on June 05, 2008 at 11:46 AM

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