Here’s my go at it. Let me know what other approaches you can think of.

@ericasadun If we extend UnicodeScalar to conform to ForwardIndexType, we can create and map a Range: https://t.co/coms3wWFIr

— Nate Cook (@nnnnnnnn) September 14, 2015

@nnnnnnnn @ericasadun Swift can infer UnicodeScalar as following:
let alphabet = ("A"…"Z" as Range).map { String($0) }

— Norio Nomura (@norio_nomura) September 14, 2015

@ericasadun You shouldn't use removeFirst() as its O(n) on arrays, you can just return the letters.generate() Gen which is definitely O(1)

— Kametrixom (@Kametrixom) September 14, 2015

@ericasadun @SwiftSandbox

let uniLetters = (UnicodeScalar("A").value…UnicodeScalar("Z").value).map({ String(UnicodeScalar($0)) })

— Nyx (@Nyx_Reloaded) September 14, 2015