// Part 1
extension UInt {
    public init(bytes: Bytes) {
        self = 0
        for byte in bytes {
            self <<= 8
            self |= UInt(byte)
        }
    }
}

// Part 2
public typealias Bytes = [UInt8]
extension UInt {
    public init(bytes: Bytes) {
        self = 0
        for byte in bytes {
            self <<= 8
            self |= UInt(byte)
        }
    }
}

$ swift
Welcome to Apple Swift version 3.0.2 (swiftlang-800.0.63 clang-800.0.42.1). Type :help for assistance.
  1> // Part 1 
  2. extension UInt { 
  3.     public init(bytes: Bytes) { 
  4.         self = 0 
  5.         for byte in bytes { 
  6.             self <<= 8 
  7.             self |= UInt(byte) 
  8.         } 
  9.     } 
 10. }
error: repl.swift:3:24: error: use of undeclared type 'Bytes'
    public init(bytes: Bytes) {
                       ^~~~~


  1> // Part 2 
  2. public typealias Bytes = [UInt8] 
  3. extension UInt { 
  4.     public init(bytes: Bytes) { 
  5.         self = 0 
  6.         for byte in bytes { 
  7.             self <<= 8 
  8.             self |= UInt(byte) 
  9.         } 
 10.     } 
 11. }
Segmentation fault: 11