String Find in Swift

In Swift, you can find the range of a substring using range(of:), which comes from Foundation, so a standalone file needs import Foundation at the top:

s.range(of: sub)                                    // returns Range? of first occurrence, or nil if not found
s.range(of: sub, options: .backwards)              // returns Range? of last occurrence
s.range(of: sub, range: fromIdx..

Here are some examples:

import Foundation

let sentence = "Hello World"
if let range = sentence.range(of: "World") {
    let idx = sentence.distance(from: sentence.startIndex, to: range.lowerBound)
    print(idx)  // 6
}

print(sentence.range(of: "xyz"))  // nil  (not found)

The index returned is the position of the first character of the found substring.