Generic uniq function in Swift

uniq.swift

// uniq func for Swift 1.2

func uniq<C: ExtensibleCollectionType where C.Generator.Element: Hashable>(collection: C) -> C {
    var seen:Set<C.Generator.Element> = Set()
    
    return reduce(collection, C()) { result, item in
        if seen.contains(item) {
            return result
        }
        
        seen.insert(item)
        return result + [item]
    }
}

uniq([1, 2, 2, 2, 3, 4, 4]) // > [1, 2, 3, 4]
uniq("aaabccc") // > "abc"

uniq_superceded.swift

// uniq func for Swift 1.1

func uniq<C: ExtensibleCollectionType where C.Generator.Element: Hashable>(collection: C) -> C {
    var seen: [C.Generator.Element: Void] = [:]
    
    return reduce(collection, C()) { result, item in
        if seen[item] != nil {
            return result
        }
        
        seen[item] = ()
        return result + [item]
    }
}

uniq([1, 2, 2, 2, 3, 4, 4]) // > [1, 2, 3, 4]
uniq("aaabccc") // > "abc"

With thanks to https://twitter.com/brentdax for the correct dictionary declaration incantation.
var seen: [C.Generator.Element: Void]() doesn't work. The following does:
var seen: [C.Generator.Element: Void] = [:]

sweet!

This is working for me in Swift 2, using a protocol extension:

extension ExtensibleCollectionType where Self.Generator.Element: Hashable {
    func uniq() -> Self {
        var seen:Set<Self.Generator.Element> = Set()
        return reduce(Self()) { result, item in
            if seen.contains(item) {
                return result
            }
            seen.insert(item)
            return result + [item]
        }
    }
}

then

print([1, 2, 2, 2, 3, 4, 4].uniq()) // > [1, 2, 3, 4]
print(String("aaabccc".characters.uniq())) // > "abc"

(Note that the String usage changed, because it's no longer CollectionType in Swift 2.)

I updated it for Xcode 7 beta 4, and wrote about it here: http://kelan.io/2015/collection-extensions-in-swift-uniq-and-tapdescription/