I expected the following code to compile:
struct Wrapper<Element>: BidirectionalCollection {
var elements: [Element]
var startIndex: Int { return 0 }
var endIndex: Int { return elements.count }
func index(after index: Int) -> Int { return index + 1 }
func index(before index: Int) -> Int { return index - 1 }
subscript(position: Int) -> Element {
return elements[position]
}
}
However, I got a long list of errors. I tried adding this:
extension Wrapper {
subscript(bounds: Range<Int>) -> BidirectionalSlice<Wrapper> {
return BidirectionalSlice(base: self, bounds: bounds)
}
}
But not Xcode shows an interesting error message: “Type
`Wrapper<Element>.Index` does not conform to protocol `Comparable`”. Surely,
Wrapper<Element>.Index is just Int which can be inferred from the startIndex
property, for example. I tried setting the Index type explicitly:
struct Wrapper<Element>: BidirectionalCollection {
typealias Index = Int
...
}
Now the code finally compiles. Bug?_______________________________________________
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