Swiftでは++が使えないので、その代わりにcount変数をカウントアップする関数で代用 #minna_de_swift

CodePiece.swift

let fibonacci = sequence(state: (current: 0, next: 1)) { state -> Int in
    defer {
        state = (current: state.next, next: state.current + state.next)
    }
    return state.current
}

let values = Array(fibonacci.prefix(13))

var count = 0
func index() -> Int {
    defer {
        count += 1
    }
    return count
}

print(values[index()]) // 0
print(values[index()]) // 1
print(values[index()]) // 1
print(values[index()]) // 2
print(values[index()]) // 3
print(values[index()]) // 5
print(values[index()]) // 8
print(values[index()]) // 13
print(values[index()]) // 21
print(values[index()]) // 34
print(values[index()]) // 55
print(values[index()]) // 89
print(values[index()]) // 144