How to parse array from description in Swift 4?

Question

I\'m learning Swift 4, and I have an algorithm that output the base 64 description of an array, like that:

extension String {

    func fromBase64()         


        

Answer 1

You should not rely on the description method to produce a particular predictable output, better use a JSON encoder for that purpose (example below).

Having said that, "[1, 2, 4, 65]" happens to be a valid JSON array, and a JSON decoder can parse it back to an integer array:

let output = "[1, 2, 4, 65]"
do {
    let array = try JSONDecoder().decode([Int].self, from: Data(output.utf8))
    print(array) // [1, 2, 4, 65]
} catch {
    print("Invalid input", error.localizedDescription)
}

Here is a self-contained example how you can reliably encode and decode an integer array to/from a Base64 encoded string.

// Encode:
let intArray = [1, 2, 4, 65]
let output = try! JSONEncoder().encode(intArray).base64EncodedString()
print(output) // WzEsMiw0LDY1XQ==

// Decode:
let output = "WzEsMiw0LDY1XQ=="
if let data = Data(base64Encoded: output),
    let array = try? JSONDecoder().decode([Int].self, from: data) {
    print(array) // [1, 2, 4, 65]
} else {
    print("Invalid input")
}

Answer 2

Here is the way you can convert your string into Int array:

var toString = output.fromBase64() //"[1, 2, 4, 65]"
if let str = toString {
    let chars = CharacterSet(charactersIn: ",][ ")
    let split = str.components(separatedBy: chars).filter { $0 != "" }.flatMap { Int($0)}
    print(split)  //[1, 2, 4, 65]
}