[swift-evolution] [swift-evolution-announce] [Review] SE-0089: Replace protocol<P1, P2> syntax with Any<P1, P2>

Fri May 27 11:31:48 CDT 2016

> Am 27.05.2016 um 18:28 schrieb Matthew Johnson <matthew at anandabits.com>:
> 
> 
> 
> Sent from my iPad
> 
> On May 27, 2016, at 11:18 AM, Austin Zheng <austinzheng at gmail.com <mailto:austinzheng at gmail.com>> wrote:
> 
>> Here's a strawman idea.
>> 
>> What if we go with '&' and 'where', but we enclose the whole thing in parentheses?
>> 
>> (class & Protocol1 & Protocol2 where .Foo == Int, .Bar : Baz)
>> 
>> There are a couple of reasons I propose this syntax:
>> 
>> - It makes it very clear where the definition of the type begins and ends. I understand people really despise angle brackets, but I really want some way to visually delineate the boundaries of the type. Plus, I imagine it makes syntax a little easier to parse and preemptively forbids some ambiguities.
>> 
>> - It's a structural, not nominal, type, like a tuple, so it uses parens as well. This reserves "<" and ">" for generic types.
>> 
>> - The '&' is easily understood - "Protocol1" *and* "Protocol2". It's also a signal that order doesn't matter - just like how order matters with things that use commas, like argument lists, tuples, and array members, order doesn't generally matter with bitwise or logical 'and' operators.
>> 
>> - If we ever decide to have union types, we have a very elegant third form of nominal type syntax that naturally falls out: (MyClass1 | MyClass2 | MyClass3).
>> 
>> Thoughts?
> 
> Generally in favor.  But I would not require the parentheses.  I believe they would be allowed optionally automatically, just as (Int) is the same as Int (because single element tuples don't exist and the underlying type is used directly instead).  It seems better to leave parentheses up to a matter of style.

Totally agree. Parentheses should only be required to resolve ambiguities.

-Thorsten

> 
> 
>> 
>> Austin
>> 
>> 
>>> On May 27, 2016, at 9:07 AM, Thorsten Seitz via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> 
>>>> Am 27.05.2016 um 16:54 schrieb Matthew Johnson <matthew at anandabits.com <mailto:matthew at anandabits.com>>:
>>>> 
>>>>> 
>>>>> On May 27, 2016, at 8:18 AM, Thorsten Seitz via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>> Personally I think `&` is more lightweight (and it is established in other languages like Ceylon and Typescript) and `where` is more expressive (and established in Swift for introducing constraints), so I would stay with these.
>>>> 
>>>> I agree.  If we can make `&` with `where` work syntactically it would be nice to go in this lighter weight direction.  If we decide to do that the question then becomes what to do with `protocol`.  Would it be feasible to replace it with `&` in Swift 3 if we decide on that direction?
>>> 
>>> Yep. `protocol` should be replaced with `&` in that case.
>>> 
>>> -Thorsten
>>> 
>>> 
>>>> 
>>>>> 
>>>>> -Thorsten
>>>>> 
>>>>> 
>>>>>> Am 27.05.2016 um 14:34 schrieb Vladimir.S <svabox at gmail.com <mailto:svabox at gmail.com>>:
>>>>>> 
>>>>>> Btw, in case we have `where` keyword in syntax related to types/protocols (when defining constrains. and not some symbol like '>>'.. don't know, for example), why we can't have 'and' keyword also when discuss the syntax of type/protocol conjunction?
>>>>>> I.e.
>>>>>> 
>>>>>> let x: P and Q
>>>>>> let x: P and Q where P.T == Q.T
>>>>>> let x: P and Q and R
>>>>>> 
>>>>>> or, for consistency, as I understand it, we should have
>>>>>> let x: P & Q >> P.T == Q.T
>>>>>> 
>>>>>> On 27.05.2016 11:55, Thorsten Seitz via swift-evolution wrote:
>>>>>>> We could just write
>>>>>>> 
>>>>>>> let x: P & Q
>>>>>>> instead of
>>>>>>> let x: Any<P, Q>
>>>>>>> 
>>>>>>> let x: Collection where .Element: P
>>>>>>> instead of
>>>>>>> let x: Any<Collection where .Element: P>
>>>>>>> 
>>>>>>> let x: P & Q where P.T == Q.T
>>>>>>> instead of
>>>>>>> let x: Any<P, Q where P.T == Q.T>
>>>>>>> 
>>>>>>> let x: P & Q & R
>>>>>>> instead of
>>>>>>> let x: Any<P, Q, R>
>>>>>>> 
>>>>>>> let x: Collection
>>>>>>> instead of
>>>>>>> let x: Any<Collection>
>>>>>>> 
>>>>>>> 
>>>>>>> This would avoid the confusion of Any<T1, T2> being something completely
>>>>>>> different than a generic type (i.e. order of T1, T2 does not matter whereas
>>>>>>> for generic types it is essential).
>>>>>>> 
>>>>>>> 
>>>>>>> -Thorsten
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>>> Am 26.05.2016 um 20:11 schrieb Adrian Zubarev via swift-evolution
>>>>>>>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org>>>:
>>>>>>>> 
>>>>>>>> Something like |type<…>| was considered at the very start of the whole
>>>>>>>> discussion (in this thread
>>>>>>>> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160502/016523.html <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160502/016523.html>>),
>>>>>>>> but it does not solve the meaning of an existential type and also might
>>>>>>>> lead to even more confusion.
>>>>>>>> 
>>>>>>>> From my perspective I wouldn’t use parentheses here because it looks more
>>>>>>>> like an init without any label |Type.init(…)| or |Type(…)|. I could live
>>>>>>>> with |Any[…]| but this doesn’t look shiny and Swifty to me. Thats only my
>>>>>>>> personal view. ;)
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> --
>>>>>>>> Adrian Zubarev
>>>>>>>> Sent with Airmail
>>>>>>>> 
>>>>>>>> Am 26. Mai 2016 bei 19:48:04, Vladimir.S via swift-evolution
>>>>>>>> (swift-evolution at swift.org <mailto:swift-evolution at swift.org> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org>>) schrieb:
>>>>>>>> 
>>>>>>>>> Don't think {} is better here, as they also have "established meaning in
>>>>>>>>> Swift today".
>>>>>>>>> 
>>>>>>>>> How about just Type(P1 & P2 | P3) - as IMO we can think of such
>>>>>>>>> construction as "creation" of new type and `P1 & P2 | P3` could be treated
>>>>>>>>> as parameters to initializer.
>>>>>>>>> 
>>>>>>>>> func f(t: Type(P1 & P2 | P3)) {..}
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> On 26.05.2016 20:32, L. Mihalkovic via swift-evolution wrote:
>>>>>>>>> > How about something like Type{P1 & P2 | P3} the point being that "<...>" has an established meaning in Swift today which is not what is expressed in the "<P1,P2,P3>" contained inside Any<P1, P2,P3>.
>>>>>>>>> >
>>>>>>>>> >> On May 26, 2016, at 7:11 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org>>> wrote:
>>>>>>>>> >>
>>>>>>>>> >>
>>>>>>>>> >>> on Thu May 26 2016, Adrian Zubarev <swift-evolution at swift.org <mailto:swift-evolution at swift.org> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org>>> wrote:
>>>>>>>>> >>>
>>>>>>>>> >>> There is great feedback going on here. I'd like to consider a few things here:
>>>>>>>>> >>>
>>>>>>>>> >>> * What if we name the whole thing `Existential<>` to sort out all
>>>>>>>>> >>> confusion?
>>>>>>>>> >>
>>>>>>>>> >> Some of us believe that “existential” is way too theoretical a word to
>>>>>>>>> >> force into the official lexicon of Swift. I think “Any<...>” is much
>>>>>>>>> >> more conceptually accessible.
>>>>>>>>> >>
>>>>>>>>> >>>
>>>>>>>>> >>> This would allow `typealias Any = Existential<>`. * Should
>>>>>>>>> >>> `protocol A: Any<class>` replace `protocol A: class`? Or at least
>>>>>>>>> >>> deprecate it. * Do we need `typealias AnyClass = Any<class>` or do we
>>>>>>>>> >>> want to use any class requirement existential directly? If second, we
>>>>>>>>> >>> will need to allow direct existential usage on protocols (right now we
>>>>>>>>> >>> only can use typealiases as a worksround).
>>>>>>>>> >>
>>>>>>>>> >> --
>>>>>>>>> >> Dave
>>>>>>>>> >>
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