You can avoid first initialising the array to placeholder values, if you go through pointers in a slightly convoluted manner, or via the new Array
constructor introduced in Swift 3:
Swift 3
let data = "foo".data(using: .utf8)!
// new constructor:
let array = [UInt8](data)
// …or old style through pointers:
let array = data.withUnsafeBytes {
[UInt8](UnsafeBufferPointer(start: $0, count: data.count))
}
Swift 2
Array(UnsafeBufferPointer(start: UnsafePointer<UInt8>(data.bytes), count: data.length))