Collection.rotated(toStartAt:) approach.

collection_rotated_sketch.swift

extension Collection {
	func rotated(toStartAt newStart: Index) -> AnyCollection<Element> {
		self[newStart...] + self[..<newStart] // ❌ “Cannot convert return
		// expression of type `SubSequence` to return type `AnyCollection<Element>`.”
		//
		// ❌ “Referencing operator function `+` on `RangeReplaceableCollection`
		// requires that `SubSequence` conform to `RangeReplaceableCollection`.”
	}
}