Weakness of "requires public"

[Paul Benedict]

Malachi, it's not a matter of how one knows or even if one should know.
It's not even a matter of how things should be but how things are. There
are distributions that have a main library and companion libraries.
Sometimes these are coded in a way such that the main library is API that
knows about types in the supplemental API. If the supplemental API is
available at runtime, the primary API can leverage it. This is typically
done via testing with Class.forName() to load classes dynamically and
reflective method calling.

In today's world, I can tell Maven that I neither need to compile nor run
with the supplemental library. I can completely exclude it from my build
path. If for some reason, the author of such Maven module has the
transitive dependencies incorrect, I can correct them.

My point is there is no such parallel in Jigsaw to completely exclude a
transitive module from compile and run time.

Cheers,
Paul

On Tue, Jul 26, 2016 at 5:33 PM, Malachi de Ælfweald <malachid at gmail.com>
wrote:

> If your M3 depends on M2, how do you know what the current implementation
> of M2 does behind the scenes? How do you know it isn't depending on M1?
>
> To give a concrete example, if an app depends on GSON, why should they
> know about all the internals of how the GSON library is written to know
> which method calls will call which other modules/libraries?
>
> If you want optional things at compile time, that seems more like a plugin
> approach (a'la ServiceLoader) where you are controlling which items get
> loaded - but that's different than what some black box does internally.
>
>
>
>
> Malachi de Ælfweald
> http://www.google.com/profiles/malachid
>
> On Tue, Jul 26, 2016 at 3:12 PM, Paul Benedict <pbenedict at apache.org>
> wrote:
>
>> Alex, that's one half of the puzzle. The other half would be excluding it
>> at compile time too. In the scenario I was giving Remi, I do not even need
>> M1 at compile time. It can be completely eliminated from my project.
>>
>> Cheers,
>> Paul
>>
>> On Tue, Jul 26, 2016 at 4:58 PM, Alex Buckley <alex.buckley at oracle.com>
>> wrote:
>>
>> > On 7/26/2016 2:50 PM, Paul Benedict wrote:
>> >
>> >> Okay, I accept your scenario for what it is. You created a very nice
>> >> example to illustrate your point where everything must be one, but
>> >> you know not every project is like this. The whole discussion with
>> >> Joda Time was based on having additional functionality from classes
>> >> which were optional at runtime. I am raising the issue that
>> >> transitive dependencies are also sometimes optional at runtime. Where
>> >> is the relief for this scenario? It doesn't exist -- but it should.
>> >>
>> >
>> > The #CompileTimeDependences proposal allows transitive dependencies to
>> > be optional at run time. It's the 'requires public static ...' use case.
>> >
>> > Alex
>> >
>>
>
>