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iOS Closures in Swift 2 First Class Functions Higher Order Functions

Sheng Wei
Sheng Wei
4,382 Points
Posted by Sheng Wei
Sheng Wei
4,382 Points

[Help!] Not sure how to return the characters property in this closure

Im not sure about the syntax to return the operation, help please. Thank You!

functions.swift 
// Enter your code below
extension String {
    func modify(operation: String -> String) -> String {
         return operation(self)
    }
}

func firstLetter(characters: String) -> String {
     return operation.characters(0)
}

1 Answer

jcorum
jcorum
71,830 Points

Wei, your extension was great! For the 2nd method you need to return a String, but a String is a collection of characters, and so you have to first get the first character, and then cast that to a String.

extension String {
    func modify(operation: String -> String) -> String {
         return operation(self)
    }
}
func firstLetter(str: String) -> String {
    return String(str.characters.first!)
}

let value = "Swift".modify(firstLetter)

Finally, you need to use both methods on the String literal "Swift".

P.S., note that first returns an optional, so I just forcibly unwrapped it as the challenge wants us to try it on a non-empty String literal. But in production code you wouldn't want to do it this way.