Re: [equinox-dev] Class visibility without declared dependency

[Stephan Herrmann <stephan.herrmann@xxxxxxxxx>]

On 07/27/2013 05:12 PM, Neil Bartlett wrote:
> > Quick experiments with Export-Package & include seem to indicate,
> > that from multiple exports of the same package only the last one survives.
>
> What kind of experiments?

bundle Provider:
Export-Package: provider;include:="C1";my-attr="foo",
 provider;include:="C2";my-attr="bar"

bundle Client:
Import-Package: provider

Activator uses classes provider.C1, provider.C2, provider.C3.
Only C2 is found at runtime.

But I see now that this is an incomplete experiment, see below.

> Export-Package can indeed export the same package multiple times with
> different attributes. For example it's possible to exports multiple
> versions:
>
>      Export-Package: org.foo; version=1.0, org.foo; version=2.0
>
> and this bundle can be wired by importers importing either version
> [1.0,2) OR [2.0,3). That is, the importer may match any one of the
> exports, they do not need to match all.

Maybe the problem is at the import side, not the export side.
When I modify the client declaration:
  Import-Package: provider;my-attr="foo"
then C2 is no longer found, but C1 is. Makes sense.

I had implicitly hoped that omitting my-attr would lead to importing
the merge of both export declarations. This seems not to be the case.

I interpret this as:
- a bundle may multiply export the same package with different attributes
- a bundle can import the same package only once, selection will be based
  on attribute matching (or s.t. like last-save-wins if attr. not specified)
Please correct me if this is wrong.

This gets me thinking how I can group the necessary declarations
so that each importing bundle will find a matching and exhaustive
export declaration.

thanks!
Stephan