alphabet.swift

// You can create a countable range of any strideable type that has
// an integer stride.
let digits = Array(0...9)

// This extension gives those properties to `UnicodeScalar`:
extension UnicodeScalar : Strideable { 
    public func advanced(by n: Int) -> UnicodeScalar { 
        return UnicodeScalar(UInt32(Int(value) + n))!
    } 
    public func distance(to other: UnicodeScalar) -> Int { 
        return Int(other.value) - Int(value) 
    } 
} 

// The type inference doesn't quite work here (the compiler assumes `String` for
// the literals), so you need to supply the `UnicodeScalar` type somewhere:
let alphabet = Array(("a" as UnicodeScalar)..."z")
print(alphabet)
// ["a", "b", "c", "d", "e", "f", "g", ...]