How do you split a String into a [String] and not [Substring]?

Question

Consider the following extension:

extension Array where Element == String {
    func foo(){
    }
}

And consider the following string that I want to split so I can use the extension...

let string = "This|is|a|test"
let words = string.split(separator: "|")

The problem is words is a [Substring] and not [String] so I can't call foo() on it.

So in Swift 4, how do I split a string to return a [String] and not a [Substring]?

Answer 1

As Leo said above, you can use components(separatedBy:)

let string = "This|is|a|test"
let words = string.components(separatedBy: "|")
words.foo()

instead, that returns a [String].

If you want to stick with split() (e.g. because it has more options, such as to omit empty subsequences), then you'll have to create a new array by converting each Substring to a String:

let string = "This|is|a|test"
let words = string.split(separator: "|").map(String.init)
words.foo()

Alternatively – if possible – make the array extension method more general to take arguments conforming to the StringProtocol protocol, that covers both String and Substring:

extension Array where Element: StringProtocol {
    func foo(){
    }
}