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

Jordan Rose jordan_rose at apple.com
Thu Jun 23 22:55:40 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’ve gone on record before as against this syntax, although when I set out earlier today to record my usual rebuttal I found that it really was mostly a matter of taste. Yes, this looks weird to me:

let callback: (Data) -> NSCoding & NSCopying

but I’m sure the infix ‘->’ for functions looked weird to everyone the first time they saw it as well, and it really is pretty clear in argument position.

However, I did remember one issue, which was brought up on the previous mega-thread: if we do want to generalize protocol values <https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md#generalized-existentials>, we’re going to want something that’s essentially “a type with a ‘where’ clauses in it”. I really don’t want to force people to use a typealias to spell such a type, but at the same time I want that where clause to be clearly attached to the type. (As brought up before the return position of a function is currently ambiguous with SE-0081 <https://github.com/apple/swift-evolution/blob/master/proposals/0081-move-where-expression.md>.)

Despite the lightweightedness and the well-prepared proposal by Adrian and Austin, the lack of bracketing <> () {} [] leads me to maintain my stance against the proposed syntax.


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