Swift 2.1 [UInt8] --utf8--> String?

Question

I know questions like this exist on both Stack Overflow and elsewhere. But it seems to have evolved a lot as well.

Given a list of UInt8 (a swift byte a

Answer 1

I actually ended up needing to do this for a stream of UInt8 and was curious how hard utf8 decoding is. It's definitely not a one liner, but through the following direct implementation together:

import UIKit

let bytes:[UInt8] = [0xE2, 0x82, 0xEC, 0x00]

var g = bytes.generate()

extension String {
    init(var utf8stream:IndexingGenerator<[UInt8]>) {
        var result = ""
        var codepoint:UInt32 = 0
        while let byte = utf8stream.next() where byte != 0x00 {
            codepoint = UInt32(byte)
            var extraBytes = 0
            if byte & 0b11100000 == 0b11000000 {
                extraBytes = 1
                codepoint &= 0b00011111
            }
            else if byte & 0b11110000 == 0b11100000 {
                extraBytes = 2
                codepoint &= 0b00001111
            }
            else if byte & 0b11111000 == 0b11110000 {
                extraBytes = 3
                codepoint &= 0b00000111
            }
            else if byte & 0b11111100 == 0b11111000 {
                extraBytes = 4
                codepoint &= 0b00000011
            }
            else if byte & 0b11111110 == 0b11111100 {
                extraBytes = 5
                codepoint &= 0b00000001
            }
            for _ in 0..