diff.swift

extension Array where Element: Equatable {
    typealias Enumerated = (Int, Element)
    func diff(fromNewArray newArray: [Element]) -> (added: [Enumerated], deleted: [Enumerated]) {
        // 削除分: newArrayにはないもの
        var added: [Enumerated] = []
        var deleted: [Enumerated] = []
        for (i, e) in newArray.enumerated() {
            guard i < self.count else {
                added.append((i, e))
                continue
            }
            if !self.contains(e) {
                added.append((i, e))
            }
        }
        // 追加分: newArrayにしかないもの
        for (i, e) in self.enumerated() {
            guard i < self.count else {
                deleted.append((i, e))
                continue
            }
            if !newArray.contains(e) {
                deleted.append((i, e))
            }
        }
        return (added, deleted)
    }
}