Motivation for type-level exports

[mark.reinhold at oracle.com]

2011/11/8 13:40 -0800, mark.reinhold at oracle.com:
> 2011/11/4 10:04 -0700, njbartlett at gmail.com:
>> ...
>> 
>> Restricting visibility of a type that is currently public does not seem
>> like a requirement that could be motivated by JDK modularisation, since
>> it would break compatibility for any existing consumers of that
>> type.
> 
> Correct.
> 
>> It's possible that there is a need to introduce *new* types in
>> the JDK modules that will be public but non-exported, though that seems
>> unlikely.
> 
> Agreed.
> 
> We haven't, in fact, run across any situations in the JDK modularization
> work that absolutely require type-level exports.
> 
>> In application code, why not just have package-level exports,
>> i.e. entire packages are either exported or private?
> 
> Package-level imports are certainly simpler, and they do appear adequate

s/imports/exports/ (!)

> for many, if not most, use cases both in the JDK and in applications.
> 
> When we introduced export clauses into the prototype Alex argued, and
> I agreed [1], that we should use type granularity rather than package
> granularity.  That approach is theoretically appealing but it turns out
> to be difficult to implement efficiently (as we learned from Mandy's
> prototype work last summer); it also makes it more difficult to reason
> about the semantics of module graphs.
> 
> I strongly suspect that we'll drop type-level exports unless some actual
> use cases crop up.
> 
> - Mark
> 
> 
> [1] http://mail.openjdk.java.net/pipermail/jigsaw-dev/2011-April/001224.html