[swift-evolution] Property with class and protocol type

[Adrian Zubarev]

I guess you don’t understand that a so called proposal should have enough details to explain the proposed behavior to someone who is not the author of the proposal. You’re offering is fine but a few unexplained lines of your gist wouldn’t make through a proposal review at all. I rather give a book to someone to read then a few unexplained samples where you’d scratch your head trying to figure out what my intention might mean. I’m sure you learned math theories not by looking at complex formulas without reading any explanation about what its parameter and mathematical-syntax mean, if you ever did. I’m not trying to insult here anyone so don’t take that to personal!

That said, I’m strongly against that ugly and not swifty looking _[ ] syntax. ClassName[Params] is okay but an empty _[ ] is just ugly. Again this is my personal opinion and it’s up to the core team to decide.

If we’d look at your so called ‘absurd’ example and imagine the shorthand syntax support class-requirements like proposed:

let v: UIViewController & UIWindow & UITableViewDelegate

there is definitely one thing that should happen for sure:

complier should raise an error at compile time right after typing out the whole existential type or even after UIViewController & UIWindow.
such an error message would provide enough informations for you that an existential type with class requirements cannot be composed with two classes (without nesting existentials)
Lets try nesting:

let v: UIViewController & (UIWindow & UITableViewDelegate)

this will again raise an error and tell you that UIViewController and UIWindow has no subtyping-relationship and are incompatible class types.

If you tried creating an existential type without reading and learning from docs first, lets say it’s your own fault that you will end up with these error messages, but either way you’d quickly learn how they behave.

That said, merging types to existentials with an infix & operator does look swifty to me (my opinion again) and is intuitive enough for that behavior.

You may ask for | operator, but this is a different story here. I’d support it to be able reduce overloading:

func foo(value: OneOf<A, B, C>) { … }
func foo(value: A | B | C) { … }

// Imagine AnyStruct and AnyEnum (they probably won't make it into Swift)
typealias AnyValue = AnyStruct | AnyEnum

// almost `Any`, we miss tuples and closures/functions here
typealias AnyExtendible = AnyValue | AnyObject


-- 
Adrian Zubarev
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Am 15. Juni 2016 um 06:27:19, L. Mihalkovic (laurent.mihalkovic at gmail.com) schrieb:

You need 3 long paragraph to explain it, the alternative I offer requires none.

https://gist.github.com/lmihalkovic/68c321ea7ffe27e553e37b794309b051

Regards
(From mobile)

On Jun 14, 2016, at 11:44 PM, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:

One more thing for clarity:

Any-class requirement: This must be the first requirement, if present. This requirement consists of the keyword class, and requires the existential to be of any class type.

Class requirement: This must be the first requirement, if present. This requirement consists of the name of a class type, and requires the existential to be of a specific class or its subclasses. There can be only one class name constraint, and it is mutually exclusive with the any-class requirement.

Nested any<...>: This requirement consists of another any<...> construct.



-- 
Adrian Zubarev
Sent with Airmail

Am 14. Juni 2016 um 23:42:00, Adrian Zubarev (adrian.zubarev at devandartist.com) schrieb:

Which addresses the fact that nons of the proposals so far truly prevent absurde declarations like:

Let v: Any< UIViewController, UIWindow, UITableViewDelegate>
Let v: UIViewController & UIWindow & UITableViewDelegate
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