[swift-evolution] [swift-evolution-announce] [Review] SE-0095: Replace protocol<P1, P2> syntax with Any<P1, P2>

Jordan Rose jordan_rose at apple.com
Wed Jun 1 11:51:51 CDT 2016

[Proposal: https://github.com/apple/swift-evolution/blob/master/proposals/0095-any-as-existential.md <https://github.com/apple/swift-evolution/blob/master/proposals/0095-any-as-existential.md> ]

I’m late again to this one, but the discussion’s certainly still going. I’m pretty strongly against the bare ‘A & B’ syntax, for a few reasons:

- Swift doesn’t use ‘&’ for anything except bitwise AND. In particular, it didn’t get picked for set intersection.

- In theory people are allowed to overload ‘&’ to operate on types. That doesn’t make sense for all types, but you could probably come up with a particular type hierarchy or use of generics where it does make sense.

- I don’t like types with spaces in them when the spaces aren’t bracketed in some way. This is entirely an aesthetic objection, of the form “I don’t naturally read that as a type, or even as a single unit, when looking at code.” This isn’t a great objection because someone could have said it about `[Int]` or `Int?` as well. (It would be a more realistic objection if some of our brackets weren’t “<" and “>”.)

And I still support the ‘Any’ syntax, despite the “order doesn’t matter” problem:

- It’s consistent with the existing unconstrained ‘Any’ and with the current dedicated wrapper types. If we didn’t think it was a good name for those, we wouldn’t use it there either.

- It’s easily learnable. It’s rare enough that someone wouldn’t be exposed to it right away, like Optional, Array, and Dictionary sugar, but when they do see it it’ll be obvious that it’s a type, and probably obvious that it’s special because of the “Any”.

- It’s a type; types always start with uppercase letters. (This has been said plenty by others.)

None of these are particularly strong arguments, I know, and I don’t have a good alternate suggestion. But I did want to go on record as being in favor of ‘Any’ and against a binary operator, even though that seems to put me in the minority.


> On May 24, 2016, at 11:06, Chris Lattner <clattner at apple.com> wrote:
> Hello Swift community,
> The review of "SE-0089: Replace protocol<P1,P2> syntax with Any<P1,P2>" begins now and runs through May 30. The proposal is available here:
> 	https://github.com/apple/swift-evolution/blob/master/proposals/0095-any-as-existential.md
> Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at
> 	https://lists.swift.org/mailman/listinfo/swift-evolution
> or, if you would like to keep your feedback private, directly to the review manager.
> What goes into a review?
> The goal of the review process is to improve the proposal under review through constructive criticism and contribute to the direction of Swift. When writing your review, here are some questions you might want to answer in your review:
> 	* What is your evaluation of the proposal?
> 	* Is the problem being addressed significant enough to warrant a change to Swift?
> 	* Does this proposal fit well with the feel and direction of Swift?
> 	* If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
> 	* How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
> More information about the Swift evolution process is available at
> 	https://github.com/apple/swift-evolution/blob/master/process.md
> Thank you,
> -Chris Lattner
> Review Manager
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