Motivation for type-level exports

[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
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