A Swift extension that adds a middle() method to Array using generics

SwiftArrayMiddleExtension.swift

protocol HasMiddleValue {
  
  typealias ItemType
  func middle() -> [ItemType]
  
}

extension Array: HasMiddleValue {
  
  typealias ItemType = Generator.Element
  
  func middle() -> [ItemType] {
    guard count > 0 else {
      return [ItemType]()
    }
    
    let middleIndex = count / 2
    let middleArray: [ItemType]
    
    if count % 2 != 0 {
      middleArray = [self[middleIndex]]
    } else {
      middleArray = [self[middleIndex - 1], self[middleIndex]]
    }
    
    return middleArray
  }
  
}

let bradyGirls = ["Marcia", "Janet", "Cindy"]
bradyGirls.middle()

let doubles = [1.1, 2, 3.3, 4, 5.5, 6]
doubles.middle()