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,

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(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(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\n"
} 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\n"
} else {
    print("string \(string) was not found")
}