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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