My notes on substringSwift have tedious string methods. These are common programming string modifiers and parsers:
Beginning of a string
let index = str.index(str.startIndex, offsetBy: 5)
let mySubstring = str[..<index] // Hello
Prefix:
let index = str.index(str.startIndex, offsetBy: 5)
let mySubstring = str.prefix(upTo: index) // Hello
let mySubstring = str.prefix(5) // Hello
End of a string subscripts:
let index = str.index(str.endIndex, offsetBy: -10)
let mySubstring = str[index...] // playground
Suffix:
let index = str.index(str.endIndex, offsetBy: -10)
let mySubstring = str.suffix(from: index) // playground
let mySubstring = str.suffix(10) // playground
Range in a string
let start: String.Index = str.index(str.startIndex, offsetBy: 7)
let end: String.Index = str.index(str.endIndex, offsetBy: -6)
let range: Range<String.Index> = start..<end
let mySubstring = str[range] // play