警告：'characters' is deprecated: Please use String or Substring directly

self.characters.count

解決：

let edit ="Summary"
edit.count   // 

警報：'substring(to:)' is deprecated: Please use String slicing subscript with a 'partial range upto' operator.

self.substring(to: self.index(of: Character(eT))!)

解決：

You should leave one side empty

let newStr = str[..<index]

The same stands for partial range from operators, just leave the other side empty:

let newStr = str[index...]

Keep in mind that these range operators return a Substring. If you want to convert it to a string, use String's initialization function:

let newStr =String(str[..<index])

You can read more about the new substrings here.