[swift-evolution] [Returned for Revision] SE-0095: Replace protocol<P1, P2> syntax with Any<P1, P2>

Adrian Zubarev adrian.zubarev at devandartist.com
Sat Jun 4 02:28:53 CDT 2016

I like the decision of the core team to replace protocol<…> with something like & instead. This gives us room to rethink Any<…> or come up with even better mechanism for existentials. :)

There are still a few things to consider:

AnyObject and AnyClass:
I’d prefer to drop the current AnyClass and rename AnyObject to AnyClass, where the current AnyClass would be used as AnyClass.Type.
AnyClass & SomeProtocol looks better to me than AnyObject & SomeProtocol.
What do you think?
Would nesting for class-requirement work the same as we described before?

Adrian Zubarev
Sent with Airmail

Am 2. Juni 2016 um 17:25:54, Austin Zheng via swift-evolution (swift-evolution at swift.org) schrieb:

I'm sure the list is getting sick of me making this point over and
over again :), so I'll only do it one more time: I find the lack of
delimiters far worse in terms of readability for type expressions of
any appreciable complexity than any number of `Any<>` tokens. In fact,
I'm a bit surprised the core team decided to go in this direction,
given their stance on parentheses for function types, and replacing
operators like "&&" or "||" with "and" or "or". I respect their
decision, though.

On 6/2/16, Thorsten Seitz <tseitz42 at icloud.com> wrote:
>> Am 02.06.2016 um 07:42 schrieb Austin Zheng via swift-evolution
>> <swift-evolution at swift.org>:
>> Excellent.
>> I put together a PR with a revised proposal containing the core team's
>> recommended approach. If anyone is curious they can see it here:
>> https://github.com/austinzheng/swift-evolution/blob/ef6adbe0fe09bff6c44c6aa9d73ee407629235ce/proposals/0095-any-as-existential.md
>> Since this is the de-facto second round discussion thread, I'll start with
>> my personal opinion (which is *not* reflected in the PR): the '&'
>> separators in lieu of commas are a good idea, but I would still prefer the
>> types to be wrapped in "Any<>", at least when being used as existentials.
> I'm very happy with using `&` as I find this very readable.
> I would prefer not having to wrap them into `Any<>`. While I can image
> `Any<>`, or rather `any<>`, for existentials with `where` clauses, I would
> absolutely hate having to wrap all existentials into that which would
> introduce a lot of noise.
>> My reasons:
>> - Jordan Rose brought up a good point in one of the discussion threads
>> today: a resilience goal is to allow a library to add an associated type
>> to a protocol that had none and not have it break user code. If this is
>> true whatever syntax is used for existentials in Swift 3 should be a valid
>> subset of the generalized existential syntax used to describe protocol
>> compositions with no associated types.
> If `P` is an existential there is no problem either, isn't it? No need to
> require `Any<P>`.
>> - I would rather have "Any<>" be used consistently across all existential
>> types eventually than have it only be used for (e.g.) existential types
>> with `where` constraints, or allowing two different representations of the
>> same existential type (one with Any, and one without).
> Far too much noise!
>> - I think any generalized existential syntax without delimiting markers
>> (like angle braces) is harder to read than syntax with such markers, so I
>> would prefer a design with those markers.
> I think markers are only needed if a `where` clause is present and probably
> not even then.
> -Thorsten
>> Best,
>> Austin
>>>> On Jun 1, 2016, at 10:17 PM, Chris Lattner <clattner at apple.com> wrote:
>>>> On Jun 1, 2016, at 9:53 PM, Austin Zheng <austinzheng at gmail.com> wrote:
>>>> This was indeed a very thorough review by the core team. I'll prepare a
>>>> v2 proposal with this feedback taken into account so we can continue
>>>> moving things along.
>>>> One quick question - is making whatever syntax is chosen for Swift 3
>>>> "forward-compatible" with a future generalized existential feature a
>>>> concern?
>>> Yes it is a concern, but we assume that the “X & Y” syntax will always be
>>> accepted going forward, as sugar for the more general feature that is yet
>>> to be designed.
>>> -Chris
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