SplitStringWithEqualLength.swift

extension String {
    func split(_ size: Int) -> [String] {
        return stride(from: 0, to: self.count, by: size).map { i -> String in
            let startIndex = self.index(self.startIndex, offsetBy: i)
            let endIndex = self.index(startIndex, offsetBy: size, limitedBy: self.endIndex) ?? self.endIndex
            return String(self[startIndex..<endIndex])
        }
    }
}
print("あけましておめでとうございます。今年もどうぞよろしくお願いします。".split(5))
//["あけまして", "おめでとう", "ございます", "。今年もど", "うぞよろし", "くお願いし", "ます。"]