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iOS Generics in Swift Generic Types Creating a Generic Type

Posted by Aananya Vyas
Aananya Vyas
20,157 Points

i tried using codes online to get help and through documentation m unable to use this please help?

Next, let's add functionality to use the queue. First, create an instance method named enqueue that takes an element and adds it to the end of the Queue. Omit the external argument label here. For example, given the queue: [1,4,9], calling enqueue with 7, results in [1,4,9,7]

thats the question^ (My code below)

generics.swift 
struct Queue<Element> {

    var array: [Element] = []

    var count : Int {
        return array.count
    }

    var isEmpty: Bool {
        if array.count == 0 {
            return true
        } else {
            return false
        }

    }

    class Node : Element {
        // variables
        var data: Element
        var prev: Node?

        init(data: Element){
            self.data = data
        }
    }

    // variables
    var head: Node?
    var tail: Node?

    func enqueue(e: Element){
        if head == nil && tail == nil {
            head = Node(data: e)
            head?.prev = nil
            tail = head
        } else {
            var temp = Node(data: e)
            tail?.prev = temp
            tail = temp

        }
    }


    func dequeue() -> Element{
        var result = head?.data

        if head === tail {
            head = nil
            tail = nil
        } else {
            head = head?.prev
        }
        if (result == nil){
            return "empty"
        }
        return result!
    }

}

1 Answer

miikis
miikis
44,957 Points

Hi Aananya,

You could have just asked for clarification on your earlier question, instead of creating a new one. Nonetheless, the reason you're having trouble with the Challenge is because you're over-complicating the tasks assigned.

You seem to be trying to implement a Linked-List but all the Challenge is asking you to do is to create a wrapper-struct around the array type so that the resulting structure behaves like a Queue (a First In, First Out structure). So:

  1. Your isEmpty property can just return array.isEmpty
  2. Your count property can just return array.count
  3. Your enqueue method can just array.append(element)
  4. Your dequeue method can just return array.removeFirst()

There's no need to create a Node class or mess around with head and tail properties. Let me know if that makes sense.

Aananya Vyas
Aananya Vyas
20,157 Points

swift_lint.swift:23:18: error: cannot invoke 'append' with an argument list of type '((Element).Type)' return array.append(Element) ^ swift_lint.swift:23:18: note: expected an argument list of type '(Element)' return array.append(Element) ^

it shows this in the preview

struct Queue<Element> {

    var array: [Element] = []

    var count : Int {
        return array.count
    }

    var isEmpty: Bool {
        if array.count == 0 {
            return true
        } else {
            return false
        }

    }

    mutating func enqueue(_ :Element){
    return array.append(Element)
    }
    }
miikis
miikis
44,957 Points

You forgot an argument label:

 mutating func enqueue(_ element:Element) {
    array.append(element)
}
Aananya Vyas
Aananya Vyas
20,157 Points

oops my bad thanks for the help though!