init(_:within:)

Declaration

init?(_ idx: String.Index, within target: String.UTF16View)

Parameters

• idx:

  A position in at least one of the views of the string shared by target.

• target:

  The UTF16View in which to find the new position.

Discussion

If the index passed as sourcePosition represents either the start of a Unicode scalar value or the position of a UTF-16 trailing surrogate, then the initializer succeeds. If sourcePosition does not have an exact corresponding position in target, then the result is nil. For example, an attempt to convert the position of a UTF-8 continuation byte results in nil.

The following example finds the position of a space in a string and then converts that position to an index in the string’s utf16 view.

let cafe = "Café 🍵"

let stringIndex = cafe.firstIndex(of: "é")!
let utf16Index = String.Index(stringIndex, within: cafe.utf16)!

print(String(cafe.utf16[...utf16Index])!)
// Prints "Café"