[swift] How can I encode a string to Base64 in Swift?

Swift 4.0.3

import UIKit

extension String {

func fromBase64() -> String? {
    guard let data = Data(base64Encoded: self, options: Data.Base64DecodingOptions(rawValue: 0)) else {
        return nil
    }

    return String(data: data as Data, encoding: String.Encoding.utf8)
}

func toBase64() -> String? {
    guard let data = self.data(using: String.Encoding.utf8) else {
        return nil
    }

    return data.base64EncodedString(options: Data.Base64EncodingOptions(rawValue: 0))
    }
}