Beginning Swift

Substring

SubString is for strings like what ArraySlice is for arrays: a view of a part of a string, where its startIndex and endIndex are indices into the original string. It conforms to the same protocols as String:

StringProtocol contains many of the common text operations, so when you write functions that take a string parameter you can often use StringProtocol instead to also accept substrings. When you do, you have to use generics, as shown here:

func foo<S: StringProtocol>(s: S) {
  // use 's' almost like a normal string.
}

Just as with ArraySlice, substrings keep a reference to the entire string, so when you are done processing substrings you ...