koher

let a = [[2], [3 ,5]] var iterator = a.enumerated().makeIterator() if var (i, numbers) = iterator.next() { numbers.append(0) print("\(i): \(numbers)") }

Version:

swift-4.1.1-RELEASE

Output:

0: [2, 0]

Error:

/usercode/main.swift:4:9: warning: variable 'i' was never mutated; consider changing to 'let' constant if var (i, numbers) = iterator.next() { ^