Unable to use contains within a Swift Array extension

Question

I am trying to write a simple Array extension that provides a \'distinct\' method. Here is what I have so far:

extension Array {
  func distinct() -> T[]          


        

Answer 1

Swift 1.x

The elements in an array don't have to be Equatable, i.e. they don't have be comparable with ==.

That means you can't write that function for all possible Arrays. And Swift doesn't allow you to extend just a subset of Arrays.

That means you should write it as a separate function (and that's probably why contains isn't a method, either).

let array = ["a", "b", "c", "a"]

func distinct(array: [T]) -> [T] {
    var rtn = [T]()

    for x in array {
        var containsItem = contains(rtn, x)
        if !containsItem {
            rtn.append(x)
        }
    }
    return rtn
}

distinct(array) // ["a", "b", "c"]

Update for Swift 2/Xcode 7 (Beta)

Swift 2 supports restricting extensions to a subset of protocol implementations, so the following is now allowed:

let array = ["a", "b", "c", "a"]

extension SequenceType where Generator.Element: Comparable {
    func distinct() -> [Generator.Element] {
        var rtn: [Generator.Element] = []

        for x in self {
            if !rtn.contains(x) {
                rtn.append(x)
            }
        }
        return rtn
    }
}

array.distinct() // ["a", "b", "c"]

Note how apple added SequenceType.contains using the same syntax.