How to sort a typed array in swift?

Question

I built a custom class which holds an "internal" array and offers some useful methods.

class ArrayList<T> {
  private var array : Array<T>

  public init() {
    array = Array<T>()
  }

  public func add(element : T) {
    array.append(element)
  }

  public func size() -> Int {
    return array.count
  }

  ...
}

Ok, that works fine for me so far.
But now I also want to have a method to sort the array. What I already have is the following:

public func sort(comparator : ?) {
  array = array.sort(comparator)
}

The question mark stands for the parameter type and that is my problem: Which type must the parameter have? I read something about @noescape<,> but I can't get it to work!
I'm using Swift 2.2.

vadian · Accepted Answer · 2016-09-30 11:15:09Z

1

The easiest way is the use the standard closure

public func sort(comparator : (T, T) -> Bool) {
   array.sortInPlace(comparator)
}

and constrain the generic type to the Comparable protocol

class ArrayList<T : Comparable>

Then you can use this code

let arrayList = ArrayList<Int>()
arrayList.add(5)
arrayList.add(12)
arrayList.add(10)
arrayList.add(2)

arrayList.sort { $0 < $1 }

print(arrayList.array) // [2, 5, 10, 12]

answered Sep 30, 2016 at 11:15

vadian

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3 Comments

overactor Over a year ago

Why would you restrict T to Comparable, you're disallowing non-comparable elements just because they can't be sorted with < and>? If anything, you could add an extension that only applies when T is comparable that offers a default sort function.

vadian Over a year ago

I know I just wanted to answer the question quite simply and avoid the Binary Operator < cannot be applied to... error message.

overactor Over a year ago

this will work fine without the restriction as well as long as T is Comparable. And if it isn't you shouldn't expect to be able to compare it using < and you can still compare it some other way.

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