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iOS

Posted by Danny Kilkenny
Danny Kilkenny
4,507 Points

Requesting Help For Higher Order Functions Part 2 of 3

I don't know how to use Characters to get the first letter from any given string.

Here is the code so far:

extension String {
    func modify(x: (String) -> String) -> String{
        return x(self)
    }
}

func firstLetter(s: String) -> String {

    return (s: "Danny")
}

2 Answers

Safwat Shenouda
Safwat Shenouda
12,362 Points

Hi Danny,

Thanks for providing a link to the challenge. below is the code that was accepted there as a solution:

 extension String {
    func modify(f: String -> String) -> String {
        return f(self)
    }
}
func firstLetter(s: String) -> String {

    return "\(s.characters.first!)"
}
let value = "Swift".modify(firstLetter)

Regarding your code, there minor changes needed: 1) return x("") should be return x(self) // you are extending the String class , so the function need to operate on self not a n empty string 2) you need to remove y: from your last line, so first letter takes one parameters, so you dont need to use its name. xcode didnt accept that on my side

I hope this would be helpful. Safwat

Danny Kilkenny
Danny Kilkenny
4,507 Points

Thank you for your response! That did work for me and so did your explanation on how to change the code.

Safwat Shenouda
Safwat Shenouda
12,362 Points
Safwat Shenouda
Safwat Shenouda
12,362 Points

The following code should work, but I'm not sure if it will answer your question. In function firstLetter you should put the actual logic that will get first letter, then pass the fucntion itself as a parameter to the modify function. It will be helpful f you share a link to the video or code challenge so I can see the exact problem. ''' extension String { func modify( x: (String) -> String) -> String {

    return x(self)
}

}

func firstLetter(s: String) -> String {

let firstLetter = s.characters.first!
return ("\(firstLetter)")

}

let x = "Michael" x.modify(firstLetter)

Danny Kilkenny
Danny Kilkenny
4,507 Points

Thanks for responding Safwat! I worked a little more on this and I'm closer but I'm still running into some issues. When I use this solution, it says: "Bummer! Make sure that your function signature matches the requirement specified in the directions" and the preview says 

swift_lint.swift:14:20: error: extraneous argument label 'y:' in call
let y = firstLetter(y: "Danny")

but xCode doesn't have a problem with it.

Here is the code below: 

extension String {
    func modify(x: (String) -> String) -> String {
        return x("")
    }
}

func firstLetter(y: String) -> String {
    let firstLetter = y.characters.first!
    return ("\(firstLetter)")
}

let y = firstLetter(y: "Danny")

and a link to the challenge: https://teamtreehouse.com/library/closures-in-swift-2/first-class-functions/higher-order-functions

Thanks