string - How to convert "Index" to type "Int" in Swift?

Question

I want to convert the index of a letter contained within a string to an integer value. Attempted to read the header files but I cannot find the type for Index, although it appears to conform to protocol ForwardIndexType with methods (e.g. distanceTo).

var letters = "abcdefg"
let index = letters.characters.indexOf("c")!

// ERROR: Cannot invoke initializer for type 'Int' with an argument list of type '(String.CharacterView.Index)'
let intValue = Int(index)  // I want the integer value of the index (e.g. 2)

Any help is appreciated.

Answer 1

edit/update:

Xcode 11 ? Swift 5.1 or later

extension StringProtocol {
    func distance(of element: Element) -> Int? { firstIndex(of: element)?.distance(in: self) }
    func distance<S: StringProtocol>(of string: S) -> Int? { range(of: string)?.lowerBound.distance(in: self) }
}

---

extension Collection {
    func distance(to index: Index) -> Int { distance(from: startIndex, to: index) }
}

---

extension String.Index {
    func distance<S: StringProtocol>(in string: S) -> Int { string.distance(to: self) }
}

---

Playground testing

let letters = "abcdefg"

let char: Character = "c"
if let distance = letters.distance(of: char) {
    print("character (char) was found at position #(distance)")   // "character c was found at position #2
"
} else {
    print("character (char) was not found")
}

---

let string = "cde"
if let distance = letters.distance(of: string) {
    print("string (string) was found at position #(distance)")   // "string cde was found at position #2
"
} else {
    print("string (string) was not found")
}