CODEWITHSUNDEEP
swiftsortinggenericsset
Thomas Zumsteg
Thomas Zumsteg

Reputation: 118

Sorting generic set in swift

What is the correct way to sort a generic typed Set in swift?

class CustomSet<T: Hashable>: NSObject {
    var items: Set<T>

     init(_ items: [T]) {
        self.items = Set(items)
    }

    var toSortedArray: [T] {
        //Error: Binary operator '<' cannot be applied to two 'T' operands
        return items.sort{ (a: T, b: T) -> Bool in return a < b}
    }
}

Xcode Version 7.1 beta (7B60), this is a wrapper around swifts Set type.

items.sort{$0 < $1} doesn't work

Cannot invoke 'sort' with an argument list of type '((_, _) -> _)'.

But works in xcrun swift

  1> let s = Set([4,2,3,4,6])
s: Set<Int> = {
  [0] = 6
  [1] = 2
  [2] = 4
  [3] = 3
}
  2> s.sort{$0 < $1}
$R0: [Int] = 4 values {
  [0] = 2
  [1] = 3
  [2] = 4
  [3] = 6
}

Upvotes: 0

Views: 1075

Answers (1)

matt
matt

Reputation: 535304

You need to constrain your generic placeholder to conform to Comparable (as well as Hashable, which you are already doing). Otherwise, as the error message says, we cannot guarantee that < is applicable.

class CustomSet<T: Hashable where T:Comparable>: NSObject {

Your xcrun example works because Int does conform to Comparable.

Upvotes: 1

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