I don’t see much value in moving them out of the angle brackets but preserving
the position; consider:
// status-quo:
func anyCommonElements <T: SequenceType, U: SequenceType
where
T.Generator.Element: Equatable,
T.Generator.Element == U.Generator.Element>
(lhs: T, _ rhs: U) -> Bool
// as-per proposal:
func anyCommonElements <T: SequenceType, U: SequenceType>
where
T.Generator.Element: Equatable,
T.Generator.Element == U.Generator.Element
(lhs: T, _ rhs: U) -> Bool
…not very different! Or, if you want it with fewer lines:
// status-quo:
func anyCommonElements <T: SequenceType, U: SequenceType
where T.Generator.Element: Equatable, T.Generator.Element ==
U.Generator.Element>
(lhs: T, _ rhs: U) -> Bool
// as-per proposal:
func anyCommonElements <T: SequenceType, U: SequenceType>
where T.Generator.Element: Equatable, T.Generator.Element ==
U.Generator.Element
(lhs: T, _ rhs: U) -> Bool
…still not very different!
Moving the `where` to come after “everything else" seems like an improvement
for functions:
func anyCommonElements <T: SequenceType, U: SequenceType>(lhs: T, _ rhs: U)
-> Bool
where
T.Generator.Element: Equatable,
T.Generator.Element == U.Generator.Element {
// body here...
}
…and presumably-also for type declarations:
class SomeClass<A,B,C,D,E> : BaseClass, SomeProtocol, AnotherProtocol
where
A.Something == SomethingElse,
B.Input == C.Output {
}
..,but would take some getting-used-to.
Losing the ability to write `:` constraints inline in the brackets seems a
non-starter, but perhaps constraints within the brackets could be limited to
`:` constraints?
> On Apr 6, 2016, at 1:30 PM, Developer via swift-evolution
> <[email protected]> wrote:
>
> If you've ever gotten to the point where you have a sufficiently generic
> interface to a thing and you need to constrain it, possibly in an extension,
> maybe for a generic free function or operator, you know what a pain the
> syntax can be for these kinds of operations. For example, the Swift book
> implements this example to motivate where clauses
>
> func anyCommonElements <T: SequenceType, U: SequenceType where
> T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element>
> (lhs: T, _ rhs: U) -> Bool
>
> This is noisy and uncomfortable to my eyes, and almost impossible to align
> correctly. Per a short discussion on Twitter with Joe Groff and Erica Sadun,
> I'd like so see what the community feels about moving the where clause out of
> the angle brackets. So that example becomes
>
> func anyCommonElements <T: SequenceType, U: SequenceType>
> where T.Generator.Element: Equatable, T.Generator.Element ==
> U.Generator.Element
> (lhs: T, _ rhs: U) -> Bool
>
> Or, if you're feeling ambitious, even
>
> func anyCommonElements <T, U>
> where T : SequenceType, U : SequenceType,
> T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element
> (lhs: T, _ rhs: U) -> Bool
>
> Thoughts?
>
> ~Robert Widmann
> _______________________________________________
> swift-evolution mailing list
> [email protected]
> https://lists.swift.org/mailman/listinfo/swift-evolution
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