Sequence+unique.swift

extension Sequence where Iterator.Element: Hashable {
    var unique: [Iterator.Element] {
        var checked: Set<Iterator.Element> = []
        return filter { checked.insert($0).inserted }
    }
}

extension Sequence where Iterator.Element: Equatable {
    var unique: [Iterator.Element] {
        reduce([]) { $0.contains($1) ? $0 : $0 + [$1] }
    }
}