Programming Style Guide: Code Refactoring

One of the key attributes towards code that is readable and easy on the eyes is code that is split into appropriately sized pieces. Code refactoring is does exactly that. It is very easy to write a program as one big piece of code. Of course, any program that grows becomes increasingly complicated and highly inefficient. If not controlled, it will soon reach a point where it is highly unreadable, extremely difficult to maintain & filled with bugs. Not to mention that it is inefficient too.

Refactoring code and breaking it down into smaller reusable chunks is the key. The objective is:

  1. To make code easier to read
  2. To make reusable components so that we can save on duplication of code. This will reduce the code count and make sure that any changes to the reused code are available everywhere.
  3. To lend a structure to the application. Tasks now have their own space.
  4. Build scalable and maintainable code.
  5. Build bug free code.

Let us look at an example.

Screen Shot 2017-10-16 at 11.26.26 AM

Bad Code

This code is clearly written poorly. Its difficult to read. There aren’t good whitespaces. No consistency. Even the naming conventions are poor.

The fix would be :

  • Break it down into different functions
  • Separate tasks into their own files
  • Name the different elements of the code properly.

This is how the code looks now. It has been broken down into different files.

main.cpp

#include <iostream>
#include "MathOperations.hpp"
#include "Choices.hpp"

int main(int argc, const char * argv[])
{
     float number1           = 0.0;
     float number2           = 0.0;
     Choices selectedOption  = CLEAR;
     float answer            = 0;
     float integralAnswer    = 0;

     while(EXIT != selectedOption)
     {
          //Welcome message
          std::cout<<"Welcome to Calculator Program"<<std::endl;
          std::cout<<"Choose between the following options"<<std::endl;
          std::cout<<"1. Add\n2. Subtract\n3. Multiply\n4. Divide\n5. Remainder\n6. Percentage"<<std::endl;

          //User choice
          std::cout<<"Choice: ";                               std::cin>>selectedOption;

          //Chance to enter first number
          std::cout<<"Number 1: ";                               std::cin>>number1;

          //Chance to enter second number
          std::cout<<"Number 2: ";                               std::cin>>number2;

          switch (selectedOption)
          {
               case ADDITION:
                    answer = addition(number1, number2);
                    std::cout<<"The addition of "<<number1<<" & "<<number2<<" = "<<answer<<std::endl;
                    break;
               case SUBTRACTION:
                    answer = subtraction(number1, number2);
                    std::cout<<"The subtraction of "<<number1<<" & "<<number2<<" = "<<answer<<std::endl;
                    break;
               case MULTIPLICATION:
                    answer = multiplication(number1, number2);
                    std::cout<<"The multiplication of "<<number1<<" & "<<number2<<" = "<<answer<<std::endl;
                    break;
               case DIVISION:
                    answer = division(number1, number2);
                    std::cout<<"The division of "<<number1<<" & "<<number2<<" = "<<answer<<std::endl;
                    break;
               case REMAINDER:
                    integralAnswer = remainder((int)number1, (int)number2);
                    std::cout<<"The remainder of "<<number1<<" divided by "<<number2<<" = "<<integralAnswer<<std::endl;
                    break;
               case PERCENTAGE:
                    answer = percentage(number1, number2);
                    std::cout<<"The percentage of "<<number1<<" out of "<<number2<<" = "<<answer<<span 				data-mce-type="bookmark" 				id="mce_SELREST_start" 				data-mce-style="overflow:hidden;line-height:0" 				style="overflow:hidden;line-height:0" 			></span><std::endl;
                    break;
               default:
                    break;
          }
     }
     return 0;
}

Choices.hpp

#ifndef Choices_hpp
#define Choices_hpp

#include <stdio.h>
#include <iostream>

enum Choices : unsigned short int { ADDITION = 1, SUBTRACTION, MULTIPLICATION, DIVISION, REMAINDER, PERCENTAGE, CLEAR, EXIT};

typedef enum Choices Choices;

std::istream& operator >>(std::istream &is, Choices& enumVar);

#endif

Choices.cpp

#include "Choices.hpp"

std::istream& operator >>(std::istream &is, Choices& enumVar)
{
    unsigned short int intVal;
    is>>intVal;
    switch (intVal) {
        case 1:
            enumVar = ADDITION;
            break;
        case 2:
            enumVar = SUBTRACTION;
            break;
        case 3:
            enumVar = MULTIPLICATION;
            break;
        case 4:
            enumVar = DIVISION;
            break;
        case 5:
            enumVar = REMAINDER;
            break;
        case 6:
            enumVar = PERCENTAGE;
            break;
        default:
            enumVar = EXIT;
            break;
    }
    return is;
}

MathOperations.hpp

#ifndef MathOperations_hpp
#define MathOperations_hpp

#include <stdio.h>

//Addition
float addition(float number1, float number2);

//Subtraction
float subtraction(float number1, float number2);

//Multiplication
float multiplication(   float number1, float number2);

//Division
float division(float number1, float number2);

//Remainder
int remainder(int number1, int number2);

//Percentage
float percentage(float number1, float number2);

#endif

MathOperations.cpp

#include "MathOperations.hpp"

//Addition
float addition(float number1, float number2)
{
    return number1 + number2;
}

//Subtraction
float subtraction(float number1, float number2)
{
    return number1 - number2;
}

//Multiplication
float multiplication(   float number1, float number2)
{
    return number2 * number1;
}

//Division
float division(float number1, float number2)
{
    if (number2 > 0) {
        return number1 / number2;
    }
    return 0.0;
}

//Remainder
int remainder(int number1, int number2)
{
    return number1 % number2;
}

//Percentage
float percentage(float number1, float number2)
{
    if (number2 > 0) {
        return (number1 / number2) * 100.0;
    }
    return 0.0;
}

Let us look at how this looks for Swift.
main.swift

import Foundation

var number1 : Float             = 0.0
var number2 : Float             = 0.0
var selectedOption : Choices    = Choices.CLEAR
var answer : Float              = 0.0
var integralAnswer : Int        = 0

func readNumbers(One firstNumber : inout Float, Two secondNumber : inout Float)
{
     //Chance to enter first number
     print("Number 1: \n")
     firstNumber = Choices.inputNumbers()

     //Chance to enter second number
     print("Number 2: \n")
     secondNumber = Choices.inputNumbers()
}

while(Choices.EXIT != selectedOption)
{
     //Welcome message
     print("Welcome to Calculator Program")
     print("Choose between the following options")
     print("1. Add\n2. Subtract\n3. Multiply\n4. Divide\n5. Remainder\n6. Percentage")

     //User choice
     print("Choice: \n")
     selectedOption = Choices.inputChoices()
     switch (selectedOption)
     {
          case Choices.ADDITION:
               readNumbers(One: &number1, Two: &number2)
               answer = addition_of(_value: number1, with_value: number2)
               print("The addition of \(number1) & \(number2) = \(answer)")
               break
          case Choices.SUBTRACTION:
               readNumbers(One: &number1, Two: &number2)
               answer = subtraction_of(_value: number1, from_value: number2)
               print("The subtraction of \(number1) & \(number2) = \(answer)")
               break
          case Choices.MULTIPLICATION:
               readNumbers(One: &number1, Two: &number2)
               answer = multiplication_of(_value: number1, with_value: number2)
               print("The multiplication of \(number1) & \(number2) = \(answer)")
               break
          case Choices.DIVISION:
               readNumbers(One: &number1, Two: &number2)
               answer = division_of(_value: number1, by_value: number2)
               print("The division of \(number1) & \(number2) = \(answer)")
               break
          case Choices.REMAINDER:
               readNumbers(One: &number1, Two: &number2)
               integralAnswer = remainder_of(_value: Int(exactly:number1)!, <span 				data-mce-type="bookmark" 				id="mce_SELREST_start" 				data-mce-style="overflow:hidden;line-height:0" 				style="overflow:hidden;line-height:0" 			></span>divided_by_value: Int(exactly: number2)!)
               print("The remainder of \(number1) divided by \(number2) = \(integralAnswer)")
               break
          case Choices.PERCENTAGE:
               readNumbers(One: &number1, Two: &number2)
               answer = percentage_of(_value: number1, with_respect_to_value: number2)
               print("The percentage of \(number1) out of \(number2) = \(answer)")
               break
          default:
               selectedOption = .EXIT
               break
     }
}

Choices.swift

import Foundation

enum Choices { case ADDITION, SUBTRACTION, MULTIPLICATION, DIVISION, REMAINDER, PERCENTAGE, CLEAR, EXIT}

//CLI Reading Capability
extension Choices
{
    static func inputChoices() -> Choices
    {
        let ip : String? = readLine()
        let choice : String = String(ip!)

        switch choice {
        case "1":
            return .ADDITION
        case "2":
            return .SUBTRACTION
        case "3":
            return .MULTIPLICATION
        case "4":
            return .DIVISION
        case "5":
            return .REMAINDER
        case "6":
            return .PERCENTAGE
        default:
            return .EXIT
        }
    }

    static func inputNumbers() -> Float
    {
        let ip : String? = readLine()

        let numberFormatter = NumberFormatter()
        let number = numberFormatter.number(from: ip!)

        let num : Float? = number?.floatValue
        return num!
    }
}

MathOperations.swift

import Foundation

//Addition
func addition_of(_value number1 : Float, with_value number2 : Float) -> Float
{
    return number1 + number2;
}

//Subtraction
func subtraction_of(_value number2 : Float, from_value number1 : Float) -> Float
{
    return number1 - number2;
}

//Multiplication
func multiplication_of(_value number1 : Float, with_value number2 : Float) -> Float
{
    return number2 * number1;
}

//Division
func division_of(_value number1 : Float, by_value number2 : Float) -> Float
{
    if (number2 > 0) {
        return number1 / number2;
    }
    return 0.0;
}

//Remainder
func remainder_of(_value number1 : Int, divided_by_value number2 : Int) -> Int
{
    return number1 % number2;
}

//Percentage
func percentage_of(_value number1 : Float, with_respect_to_value number2 : Float) -> Float
{
    if (number2 > 0) {
        return (number1 / number2) * 100.0;
    }
    return 0.0;
}

Discussion on Swift Extensions

As we can see that most of the code in Swift is very similar to C++. Most of the differences are basic syntactic differences. However, there is 1 feature of Swift that greatly aids code refactoring that I would like to talk about, Extensions.

Extensions allow us to add new functionality to the existing type. As the name says the type is extended. This allows us to add changes to a type in a consistent & clearly demarcated way. Developers can now neatly separate newly added components. This greatly helps in understanding the evolution of types.

“This is often referred to as versioning.”

Extensions can be used in the following ways to implement code refactoring:

  • Different sections of a type reside in their own extensions
  • Changes made to a type are made by keeping them in their own extensions
  • Step by step build up of code is done by representing each step as an independent extension. This gives clarity on how a certain end result was achieved.

Conclusion

As we can see from the sample code above (for both C++ & Swift) the program is much more readable. Code is carefully compartmentalised. Its a lot easier to read. It is a lot easier to scale too.

The reader may point out that the amount of code to achieve the same result is significantly higher, that however is a small price to pay in the long run. The biggest advantage is the scalability & the ease with which it can be done. Simply breaking code down into separate files & functions makes a huge difference. Here are some other benefits:

  • Individual files can be modified. This means one can now have a team working on different parts of the code.
  • Code is less cluttered. Changes are now spread across files & are easier to track.

We will now see how we can further improve this code in upcoming articles.

Programming Style Guide – The Need for programming standards

Programming Style Guide refers to the conventions followed while writing programs. This guide is going to be a series of blogs highlighting different programming standards. The series will try to cover as many standards as possible, focus will be on common and popular standards.

But why the need for programming standards? Standards help software developers design software in such a way that it is easy to read, understand, maintain & expand. It provides a consistent experience & also speeds up the way in which software development is done.

A program written with the best standards kept in mind is self explanatory, easy to read, can be built on, & is a stable piece of software

This specific article will act as a Content list for all the articles written as a part of this series. The examples are from the Swift & C++ programming languages.

  1. Naming Conventions
  2. Code Refactoring
  3. Programming Style Guide: Documentation
  4. Programming Style Guide: Command Query Separation

 

 

Programming Style Guide: Naming Conventions

Today we are going to look at Naming conventions you can follow while writing code.

Naming conventions lay down the basic rules for naming different elements in your code. The objectives are simple:

  • Make the element easy to read
  • Should be self explanatory
  • Should contain information in a compact and concise manner.

Ideally a well named variable or function should not need a comment to explain what it is for.

With the above objectives in mind let us look at some of the naming conventions that can be followed. The examples are from the Swift & C++ programming languages.

Naming Conventions

Camel Case Names

In camel case naming convention the entire name of the element is constructed by forming a sentence joined into a single word. So for example if we have a variable for keeping track of the price of oil in US dollars then the variable name might be priceOfOilUSD.

Here are some examples of naming conventions with the camel case.

SWIFT

var priceOfOil : Float = 23.49

C++

float priceOfOil = 3.45;
class PersonInfo
{

};

Underscore Separated Names

In the underscore separated naming convention the entire name of the element is constructed by forming a sentence joined together with the help of underscores in-between them. So if we take the example of the variable keeping track of the price of oil in US dollars the the variable name might be price_of_oil_usd.

Swift

var price_of_oil : Float = 45.71

C++

float price_of_oil = 99.87;

void print_value_of_pi()
{
     //print something
}

Names with type information

A naming convention that is quite popular is the one that mixes the previous 2 naming conventions, with the underscore used to separate the type description in the prefix. So if we take the example of the variable keeping track of the price of oil in US dollars then the variable name might be f_priceOfOil or float_priceOfOil. Either of the design styles work. The prefix is popularly abbreviated and you can create your own rules for abbreviating the type description.

This style is often referred to as the Hungarian notation. The additional information that is provided as a part of the prefix can be:

  • Whether the variable is a pointer
  • Whether the variable is an object
  • The scope of the variable
  • Type size
  • Whether the data can vary or is a constant

Swift

var f_priceOfOil : Float = 0.0

C++

float f_priceOfOil = 22.3;
int *ptr_memmoryBuffer = NULL; //ptr indicates variable is a pointer

Naming Rules

There are some rules that are typically followed while designing names for variables and  functions. Like the conventions themselves the rules are not binding but they are very useful an give the added punch that naming conventions provide.

  1. Variable names always start in lower case.
  2. Type names always start in upper case.
  3. The naming conventions is consistently applied through all the projects
  4. Names should be kept as small as possible without sacrificing on the description

Naming Strategies

As far as strategies are concerned there are multiple approaches that one can follow. Here are some potential strategies.

  • Follow one naming convention for variables and another convention for functions.
  • Let constants be all upper case
  • Prefix types with your companies initials.

Summary

The above illustrate just some of the naming conventions that can be followed. By no means are they comprehensive or complete. Also it is not necessarily true that everyone follows the above naming conventions. You may find that many software development firms have their own unique naming convention. This article should give you an an idea about naming conventions. Feel free to share some naming conventions that you have come across.

macOS & iOS IT Tool List

This list is based on questions that I have been asked by various IT admins.

It is more of a collection of tools (mainly software, but a few hardware tools too) that Enterprise IT Teams might find useful while supporting/managing Macs & iPhones in the enterprise. Some of the tools are free, while others are paid. Also, it is not necessary that all the tools will be required. Of course, some tools are not meant for troubleshooting but provide a service themselves.

The below list is not an endorsement or recommendation of any of the products mentioned. These are just some of the products I have come across. You may have to do your own research to see which tool fits your organisation’s needs. The author is not responsible for any damages or loss of data that might occur from usage of these tools.

*This list is not a complete list but an ongoing project. Feel free to share your comments on tools that you may have used & I will add them to this list.

DEPLOYMENT

DeployStudio

Munki

macOS Server – NetInstall Service. To be used along with System image Utility

PACKAGE MANAGEMENT

Iceberg

pkgbuild

Suspicious Package

REMOTE MANAGEMENT

RealVNC

TeamViewer

Apple Remote Desktop

LogMeIn

BACKUPS

macOS Server – Time Machine Service

Retrospect

Carbon Copy Cloner

Chronosync

Crash Plan

DEVICE MANAGEMENT

Centrify

JAMF Casper Suite

AirWatch

Mobile Iron

macOS Server – Profile Manager Service

Apple Configurator 2

Heat LANRev

Cisco Meraki

filewave

Absolute Software

BoxTone

Maas 360 – IBM

Tangoe

Lightspeed Systems

VIRTUALIZATION

Parallels Desktop

VMWare Fusion

Oracle VirtualBox

DISK MANAGEMENT

Tuxera

Disk Drill

APPLE APPLICATIONS FOR THIRD PARTY OS

iTunes

iCloud Control Panel

Move to iOS from Android

Migration Assistant

AUTOMATION

Workflow for iOS

Automator – Built in app for creating Workflows.

AppleScript

Command Line Script

NETWORK TROUBLESHOOTING

iNetTools

Network Diagnostics

Network Ping

Wireshark

DISPLAY

Air Squirrel

SYSTEM TROUBLESHOOTING

Install Disk – I will be talking about how to create a multi-OS install disk in a later article.

SOFTWARE MANAGEMENT

macOS Server – Caching Service

Reposado

AutoPKG

Munki

HARDWARE

Thunderbolt 1,2,3 Cables
Thunderbolt 1,2
USB-C Cable

FireWire 400/800 Cables

Portable disk with macOS installed on it. Not the same as install disk. Its an external bootable hard drive with the OS installed on it. You can plug this into any Mac & boot from the external HDD.

VGA to MiniDisplay adapter

HDMI to HDMI Cable

Thunderbolt Ethernet Bridge

USB Ethernet Bridge

Adapters for the different ports supported by Macs & iPhones

Lightning Cables

Creating multi-OS Install Disk

In this article we are going to look at how to create a multi-OS Install Disk. We are going to look at the example of creating a multi-OS Install Disk for the following versions of the OS:

  • 10.9.1
  • 10.10
  • 10.10.4
  • 10.11.5
  • 10.12
  • 10.12.1
  • 10.12.2
  • 10.12.3

The idea is to have a single disk with multiple versions of the Install Disk on it. The versions should reflect the need of the organisation.

REQUIREMENTS

  1. USB Drive at least 75GB in Size. This depends on the number of Install drives you wish to have. At the very least there should be enough space to create 2 partitions of 8 GB each. 
    While I have mentioned USB drive, it need not be restricted to that interface. You can use Thunderbolt, FireWire or even an SDXC slot for this. Ideally the port should be one that is supported on maximum possible computers.
  2. Install setup for each version of the OS for which you want to create the install disk. The setup must match the version desired.
  3. A Mac running the same major version of the OS. You can only create an install disk for 10.9.x on a Mac running OS X 10.9.x, the same applies for the other versions of the OS.

The process is the same. It’s just that it needs to be repeated.

STEPS

  1. Create 8 partitions on a USB Drive. Assume that the USB Drive is called Recovery Drive. Give the partitions names Partition 1, Partition 2,….
  2. Connect the USB Drive to a Mac running 10.9.1 or later.
  3. Make sure that the OS Installer setup is located in the Applications folder.
  4. Run the following command in the command line.
    sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/Partition\ 1 --applicationpath  /Applications/Install\ OS\ X\ Mavericks.app
  5. Rename the partition as Install disk for OS X 10.9.1, if necessary.
  6. Once completed eject the USB Drive & connect it to a Mac running 10.10
  7. Make sure that the OS Installer setup is located in the Applications folder.
  8. Run the following command in the command line.
    sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/Partition\ 2 --applicationpath  /Applications/Install\ OS\ X\ Yosemite.app
  9. Rename the partition as Install disk for OS X 10.10, if necessary.
  10. Once completed eject the USB Drive & connect it to a Mac running 10.10.4
  11. Make sure that the OS Installer setup is located in the Applications folder.
  12. Run the following command in the command line.
    sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/Partition\ 3 --applicationpath  /Applications/Install\ OS\ X\ Yosemite.app
  13. Rename the partition as Install disk for OS X 10.10.4, if necessary.
  14. Once completed eject the USB Drive & connect it to a Mac running 10.11.5 or later.
  15. Make sure that the OS Installer setup is located in the Applications folder.
  16. Run the following command in the command line.
    sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/Partition\ 4 --applicationpath  /Applications/Install\ OS\ X\ El\ Capitan.app
  17. Rename the partition as Install disk for OS X 10.11.5, if necessary.
  18. Once completed eject the USB Drive & connect it to a Mac running 10.12 or later.
  19. Make sure that the OS Installer setup is located in the Applications folder.
  20. Run the following command in the command line.
    sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Partition\ 5 --applicationpath  /Applications/Install\ macOS\ Sierra.app
  21. Rename the partition as Install disk for OS X 10.12., if necessary.
  22. Once completed eject the USB Drive & connect it to a Mac running 10.12.1 or later.
  23. Make sure that the OS Installer setup is located in the Applications folder.
  24. Run the following command in the command line.
    sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Partition\ 6 --applicationpath  /Applications/Install\ macOS\ Sierra.app
  25. Rename the partition as Install disk for OS X 10.12.1., if necessary.
  26. Once completed eject the USB Drive & connect it to a Mac running 10.12.2 or later.
  27. Make sure that the OS Installer setup is located in the Applications folder.
  28. Run the following command in the command line.
    sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Partition\ 7 --applicationpath  /Applications/Install\ macOS\ Sierra.app
  29. Rename the partition as Install disk for OS X 10.12.2, if necessary.
  30. Once completed eject the USB Drive & connect it to a Mac running 10.12.3 or later.
  31. Make sure that the OS Installer setup is located in the Applications folder.
  32. Run the following command in the command line.
    sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Partition\ 8 --applicationpath  /Applications/Install\ macOS\ Sierra.app
  33. Rename the partition as Install disk for OS X 10.12.3, if necessary.

The commands shown above might be different from what appears on your screen. A lot will depend on what you have named your partitions as, the name you may have given to the OS Installer file, and the location of the OS Installer.

The process of renaming the partitions post creation of the install disk is not necessary, but very useful because that will help you identify the appropriate partition when using the drive.

The above process is very scalable & can be done for even more versions of the OS if required.

Screen Shot 2017-04-17 at 11.11.39 AM
This diagram illustrates the layout of the different partitions on a single USB Drive.

COLLECTION TYPE, SEQUENCE TYPE & INDEXABLE TYPE – Update

This is an update to the topic covered earlier. You can read about the Protocols in detail in the original article. Collection Type, Sequence Type & Indexable Type

Most of the things are the same here are some of the changes:

  1. The Indexable protocol is now not necessarily required. All the aspects of the indexable protocol now fall under the Collection Protocol
  2. The names of the protocols have changed from SequenceType & CollectionType to Sequence & Collection
  3. The keyword Generator has been renamed to Iterator. Accordingly the generate function has been renamed makeIterator function.
  4. The collection protocol now requires the implementation of the function index, this function returns the value of the next index.

The sample code below should clarify

class CustomStack
{
    var data : [Element] = [Element]()

    func push(Element newElement : Element)
    {
        data.append(newElement)
    }

    func pop() -> Element
    {
        return data.removeLast()
    }
}

//Additional Implementations - not strictly required
extension CustomStack
{
    typealias Index = Int

    var startIndex : Index
    {
        return 0
    }

    var endIndex: Index
    {
        return (data.count - 1)
    }

    subscript (position : Index) -> Element
    {
        return data[position]
    }
}

extension CustomStack : Sequence
{
    typealias Iterator = AnyIterator

    func makeIterator() -> Iterator
    {
        var index = 0
        return AnyIterator({() -> Element? in
            if index < self.data.count
            {
                let res =  self.data[index]
                index += 1
                return res
            }
            return nil
        })
    }
}

extension CustomStack : Collection
{
    typealias SubSequence = CustomStack

    subscript (bounds: Range) -> CustomStack.SubSequence
    {
        let newStack : CustomStack = CustomStack()

        for i in bounds.lowerBound...bounds.upperBound
        {
            newStack.push(Element: data[i])
        }
        return newStack
    }

    /// Returns the position immediately after the given index.
    /// - Parameter i: A valid index of the collection. `i` must be less than
    ///   `endIndex`.
    /// - Returns: The index value immediately after `i`.
    func index(after i: Int) -> Int
    {
        if i < endIndex
        {
            return i + 1
        }
        return i
    }
}

Collection Type, Sequence Type & Indexable Type

This is for Swift Version 2.2 & earlier. I will be adding the snippet of code for the changes the Swift 3.x have introduced.

What are the Collection Type & Sequence Type Protocols?

The Collection Type, Sequence Type & Generator Type Protocols define rules that govern how different data structures or collections of data can be used, interacted with and operated within the Swift programming language. The CollectionType is a special case of the SequenceType.

Why do we need such Protocols?

Lets take the example of the Swift For-Loop.

var arrOfStrings : [String] = [String]()

arrOfStrings.append("Jill")
arrOfStrings.append("Jack")
arrOfStrings.append("John")
arrOfStrings.append("Jane")

for name in arrOfString
{
     print("The name is \(name)")
}

Now, if we have created our own data type. We would not be able to use the above for-loop as it would not conform to the … type protocols. The for-loop is expecting a data structure that acts and behaves in a way that is governed by the … protocols.

Just like the for-loop example above there are many other features within the Swift Programming Language that expect data structures to act and behave in a particular way. By designing our data structures to conform to these protocols we can make the easily compatible with the existing code and language features out there.

How do we use these protocols for our own data structures?

First we need to decide what kind of collection are we making. For the sake of this example I will create a Custom Stack.

class CustomStack<Element>
{
    var data : [Element] = [Element]()

    func push(Element newElement : Element)
    {
        data.append(newElement)
    }

    func pop() -> Element
    {
        return data.removeLast()
    }
}

The above code is very simple for the purpose of this exercise. Its a stack. Which is internally really an Array. It has functions to push data and pop data. We are now going to convert this type to a collection to conform to the CollectionType protocol.

Implementing the Indexable Protocol methods

As a first step we are going to make our CustomStack conform to the Indexable Protocol.

extension CustomStack : Indexable
{
    //INDEXABLE PROTOCOLS
    typealias Index = Int

    var startIndex : Int
    {
        return 0
    }

    var endIndex: Int
    {
        return (data.count - 1)
    }

    subscript (position : Int) -> Element
    {
        return data[position]
    }
}

The above change makes the data structure conform to the Indexable protocol. This is a requirement for it to be of type CollectionType. In order to conform to the Indexable protocol we need to implement a few computed properties. Let us look at the changes

typealias Index = Int

This line informs the system that the Indexing type for my data structure is an Int.

var startIndex : Int
{
    return 0
}

var endIndex: Int
{
    return (data.count - 1)
}

The next 2 are computed properties. Each provides the implementation of the startIndex  and endIndex properties. Note that the type for both is Int as we have declared the Index type earlier as Int.

subscript (position : Int) -> Element
{
    return data[position]
}

The last implementation is of subscript. This provides the implementation to access an Element from the Stack using the Subscript operator.

Implementing the Sequence Type Protocol

Next we will implement the Sequence Type Protocol methods.

extension CustomStack : SequenceType
{
    typealias Generator = AnyGenerator<Element>
    
    func generate() -> Generator
    {
        var index = 0
        
        return AnyGenerator(body: {() -> Element? in
            if index < self.data.count
            {
                let res =  self.data[index]
                index += 1
                return res
            }
            return nil
        })
    }
}

Let us examine this code line by line.

typealias Generator = AnyGenerator<Element>

Objects of type Generator allow us to navigate through our collection. Quite like how iterators  work in C++. This line specifies the type to be AnyGenerator for Elements.

func generate() -> Generator

Next we start the implementation of the generate function. This is required as part of the SequenceType protocol.

var index = 0

This index variable is used to track the element that is currently being accessed.

return AnyGenerator(body: {() -> Element? in
            if index < self.data.count
            {
                let res =  self.data[index]
                index += 1
                return res
            }
            return nil
        })

The return statement is the main statement. Here we are creating an object of type AnyGenerator. As an argument to the constructor call we are passing in a closure that will be used to iterate through the sequence. Note that the closure captures the index variable and holds a reference to its value even though we have left the original function.

Implementing the Collection Type Protocol

Next we will implement the Collection Type Protocol methods. We don’t really need to implement a lot in order to conform to the CollectionType protocol. In fact, if we just conform to the CollectionType protocol and use the implementations of the previous 2 extensions we should be just fine. However, for the sake of demonstration we are implementing the subscript functionality within the CollectionType.

extension CustomStack : CollectionType
{
    typealias SubSequence = CustomStack<Element>
    
    subscript (bounds: Range<CustomStack.Index>) -> CustomStack.SubSequence
    {
        let newStack : CustomStack<Element> = CustomStack<Element>()
        
        for i in bounds.startIndex...bounds.endIndex
        {
            newStack.push(Element: data[i])
        }
        return newStack
    }
}

Let us look at the code line by line.

typealias SubSequence = CustomStack<Element>

Again, as before this line indicates that the SubSequence type is actually a CustomStack.

subscript (bounds: Range<CustomStack.Index>) -> CustomStack.SubSequence

Here we start the implementation of the subscript functionality.

let newStack : CustomStack<Element> = CustomStack<Element>()
        
for i in bounds.startIndex...bounds.endIndex
{
     newStack.push(Element: data[i])
}
return newStack

The rest of the code is the implementation of the subscript range behaviour. One can have different implementations to achieve the same result.

CollectionType Video

Conclusion

As we can see, by designing our data structure to conform to a particular set of protocols. We have made it possible for our data structure to take advantages of the different features, functionalities and even API’s available within the Swift Language and the Frameworks used as a part of iOS, macOS, watchOS & tvOS development.

What to do before buying/selling Apple devices?

Apple’s devices are getting more and more popular by the day. People are really excited to get hold of the newest product that comes out of its stable. This guide walks you through some of the things you need to keep in mind while buying used devices or selling your existing device. This may not apply when buying a new product from the store for the first time, however, its still good to know these things & run your device through a checklist.

Note the checklist provided below is by no means comprehensive nor is it complete. There might be other things to keep in mind before buying &/or selling used devices, depending on the geographic area, situation, and circumstances.

Buying

Before buying a used products run them through this checklist. Some items are device specific.

  • Make sure there is no physical damage to the device. Dents, scratches, cracks, missing screws.
  • Start the device & make sure it loads up as expected.
  • Check the different user interface elements: touch screen, 3d touch, keyboard, iSight camera, speakers, home button, Microphone
  • Check the different ports: USB, Ethernet, FireWire, Thunderbolt, USB-C, HDMI, Audio-out, SD card reader, lightning connector, 30-pin connector
  • Check the power cord, adapter & charging port
  • Note the version of the OS. Eg: OS X 10.10.3
  • Note the build number
  • Check the model number. This is important for Software Upgrades/Hardware upgrades. Older hardware may have an upper limit on the hardware expansion capability &/or the ability to run latest software optimally.
  • Check the Support Coverage for your device. This is important, especially if you have to take your device in for repairs.
    https://checkcoverage.apple.com/in/en/
    https://support.apple.com/en-us/HT204308 – Find your devices Serial Number
  • Note down the serial number
  • Make sure that the device does not contain any personal data belonging to the seller. While it is the sellers responsibility to ensure this, it still is a good idea to verify that there are no accounts are signed into. This is VERY IMPORTANT for iOS Devices due to its implications on Activation Lock.
    Activation lock is used to prevent anyone from using a stolen device: https://support.apple.com/en-us/HT201365
  • Before buying please check the Activation lock status: https://www.icloud.com/activationlock/
  • Make sure there is no personal digital content in the form of Apps/Song/Movies or documents.
  • For Mac, make sure that there is no Firmware Password that is set.

Selling

The list above should give you a good idea on what you need to do while planning to sell your Apple device.

  • Delete all personal data. Make sure you have a backup of the same.
  • Remove any applications you may have installed.
  • Sign out of all accounts: Gmail, Hotmail, Facebook, iCloud, Apple ID…
  • Delete any user accounts you may have created. Leave a single admin account.
  • If you have used any Encryption service then make sure you turn off encryption before selling the device. This is more of a precaution to prevent issues that may arise in the future.
  • This article illustrates what to do if you are selling giving away iOS Devices: https://support.apple.com/en-in/HT201351
  • As a good measure, delink your Apple ID from your device. You can do this by:
    • Go to http://www.icloud.com
    • Sign in with your Apple ID
    • Click on Settings
    • Select the device you want to give away: IMG_2941
    • Click on the cross to remove it from your Apple IDIMG_2978
  • De-register from iMessage.
  • Remove any custom settings, passwords (Firmware Password) that may compromise your security or prevent the user from fully using the device.
  • As a good measure completely erase the hard drive of your device.
  • Document items such as OS Version, Serial Number for your own reference.

Enterprises may take additional steps

  • To ensure data security, Enterprises may perform Secure Erase or drive replacement to prevent recovery of corporate information, when assigning devices to employees or selling them out in the market.
  • Enterprises should also protect against Activation lock. When collecting iOS Devices, assigned to an employee who is leaving the organisation, always check to make sure that the device is not locked to the employees Apple ID.

These are some of the things that you can do to make the transaction easy on both the sides.