What is the BigO of Swift's String.count?

Question

When swift uses String.count is it:

O(n) where each time we call it we iterate through the entire String in order to count it

Answer 1

Looks like O(n) to me based on a quick Playground test.

for step in 1...10 {
    let length = step * 100000
    let string = String(repeating: "x", count: length)
    let start = Date()
    let stringLength = string.count
    let end = Date()
    print("Length: \(stringLength), time: \(end.timeIntervalSince(start))")
}

// Length: 100000, time: 0.00178205966949463
// Length: 200000, time: 0.00132298469543457
// Length: 300000, time: 0.00184988975524902
// Length: 400000, time: 0.00218689441680908
// Length: 500000, time: 0.00302803516387939
// Length: 600000, time: 0.00368499755859375
// Length: 700000, time: 0.0039069652557373
// Length: 800000, time: 0.00444602966308594
// Length: 900000, time: 0.0052180290222168
// Length: 1000000, time: 0.00539696216583252