Sequence().unique.swift

extension Sequence where Self.Iterator.Element: Hashable {
  
  func unique() -> [Self.Iterator.Element] {
    var knownElements = Set<Self.Iterator.Element>()
    
    return self.filter { element -> Bool in
      if !knownElements.contains(element) {
        knownElements.insert(element)
        return true
      }
      
      return false
    }
  }
  
}