What you’re trying to do should be equivalent to this:
protocol Toggling : Equatable {
…
}
It’s a bug that placing the constraint on ‘Self’ does not have the same effect
though; do you mind filing a JIRA?
Slava
> On Jul 29, 2017, at 12:24 PM, Ray Fix via swift-users <swift-users@swift.org>
> wrote:
>
> Hi,
>
> I had a question about defining protocols. Originally I wrote:
>
> protocol Toggling where Self: Equatable {
> static var all: [Self] { get }
> func toggled() -> Self
> mutating func toggle()
> }
>
> extension Toggling {
>
> func toggled() -> Self {
> let current = Self.all.index(of: self) ?? 0
> let next = (current + 1) % Self.all.count
> return Self.all[next]
> }
>
> mutating func toggle() {
> self = toggled()
> }
> }
>
> This resulted in a bunch of errors.
>
> Playground execution failed:
> ^
> error: Toggler.playground:7:28: error: cannot invoke 'index' with an argument
> list of type '(of: Self)'
> let current = Self.all.index(of: self) ?? 0
> ^
>
> Toggler.playground:7:28: note: expected an argument list of type '(of:
> Self.Element)'
> let current = Self.all.index(of: self) ?? 0
>
> This approach worked:
>
>
> protocol Toggling {
> static var all: [Self] { get }
> func toggled() -> Self
> mutating func toggle()
> }
>
> extension Toggling where Self: Equatable {
>
> func toggled() -> Self {
> let current = Self.all.index(of: self) ?? 0
> let next = (current + 1) % Self.all.count
> return Self.all[next]
> }
>
> mutating func toggle() {
> self = toggled()
> }
> }
>
> This version is probably better anyway but I am wondering if the first
> approach should have shown an error at the point of trying to attach the
> constraint to the protocol declaration. Any insights on this?
>
> Thank you,
> Ray Fix
>
>
>
>
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