swiftの配列からindexを循環して取得

なんてタイトルにしていいか分からなくて困った
pythonみたいに負の値でもうまくとりたいなって

extension

extension Array{
  subscript (loop index: Int) -> Element {
    let lIndex = (self.count + (index % self.count)) % self.count
    return self[lIndex]
  }
}

使い方

  let a = [1,2,3,4,5]
  for index in -10 ... 10{
    print("\(index), \(a[loop:index])")
  }
/*
index = -10, value = 1
index = -9, value = 2
index = -8, value = 3
index = -7, value = 4
index = -6, value = 5
index = -5, value = 1
index = -4, value = 2
index = -3, value = 3
index = -2, value = 4
index = -1, value = 5
index = 0, value = 1
index = 1, value = 2
index = 2, value = 3
index = 3, value = 4
index = 4, value = 5
index = 5, value = 1
index = 6, value = 2
index = 7, value = 3
index = 8, value = 4
index = 9, value = 5
index = 10, value = 1
*/

おわり

いまどきindexで配列にアクセスするな