Split String into [String] in specified characters length. swift3

String+chunkByLength.swift

public extension String {
    public func chunkByLength(_ count: UInt) -> [String] {
        var result = [String]()
        var idx = characters.startIndex
        while idx < characters.endIndex {
            let next = characters.index(idx, offsetBy: Int(count), limitedBy: characters.endIndex) ?? characters.endIndex
            if idx == next {
                break
            }
            result.append(self[idx..<next])
            idx = next
        }
        return result
    }
}