> On Feb 18, 2017, at 3:52 PM, David Sweeris <daveswee...@mac.com> wrote:
>
>
>> On Feb 18, 2017, at 13:12, Matthew Johnson <matt...@anandabits.com> wrote:
>>
>>
>>> On Feb 18, 2017, at 3:01 PM, David Sweeris <daveswee...@mac.com> wrote:
>>>
>>>
>>>> On Feb 18, 2017, at 12:41 PM, Matthew Johnson via swift-evolution
>>>> <swift-evolution@swift.org> wrote:
>>>>
>>>> ## Source compatibility
>>>>
>>>> This proposal breaks source compatibility, but in a way that allows for a
>>>> simple mechanical migration. A multi-release stratgegy will be used to
>>>> roll out this proposal to provide maximum possible source compatibility
>>>> from one release to the next.
>>>>
>>>> 1. In Swift 4, introduce the `open` keyword and the `@nonopen` attribute
>>>> (which can be applied to `public protocol` to give it the new semantics of
>>>> `public`).
>>>> 2. In Swift 4 (or 4.1 if necessary) start warning for `public protocol`
>>>> with no annotation.
>>>> 3. In the subsequent release `public protocol` without annotation becomes
>>>> an error.
>>>> 4. In the subsequent relase `public protocol` without annotation takes on
>>>> the new semantics.
>>>> 5. `@nonopen` becomes a warning, and evenutally an erro as soon as we are
>>>> comfortable making those changes.
>>>
>>> I don’t think we need @nonopen or warnings. IMHO, public/open should have
>>> the same semantics and syntax regardless of whether the declaration is a
>>> protocol or a concrete type (or a property?).
>>>
>>> Other than that nit, I can’t think of a reason to oppose this. So… +1,
>>> because I like making things as consistent as possible (also because of the
>>> reasons in the motivation).
>>
>> The purpose of using `@nonopen` for the migration is to eventually break
>> people’s code if they don’t use the migrator and don’t annotate it. If we
>> don’t do that the library may ship a version that unintentionally breaks
>> their clients (by continuing to use `public` after its meaning has changed).
>>
>>
>> It’s better to break the library before it breaks any clients. That will
>> impact many fewer developers. This can be handled automatically by the
>> migrator and will be a relatively minor inconvenience for developers who
>> don’t use it. That’s better than allowing an accidentally bad version of a
>> library from shipping.
>
> Do we need it for types? "@nonopen public class Foo {...}"?
>
> (Serious question... I don't recall if we did this phased thing for open vs
> public types)
No, because we already introduced that in Swift 3. Swift 4 has a higher bar
for breaking changes. If the core team is willing to accept the proposal
without a staged migration strategy I would not object to that. But I believe
it’s best for breaking proposals to present a staged migration strategy for the
core team to consider. That’s what this is. I wouldn’t want lack of a staged
migration strategy to sink the proposal.
>
> - Dave Sweeris
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