Creating custom operators in Swift

September 21, 2020 / Arun Patwardhan / 1 Comment

What are custom operators?

Custom operators are operators that are defined by us and are not part of the programming language natively.

We are all aware of the built in operators in the Swift Language.

Operators like: + – * % > == ! to name a few.

These operators are defined by the system. It is also possible for us to overload some of these operators. However there are situations where we would like to create our own operators that perform operations not defined by the system.

Thats exactly what Custom operators are. They are operators defined by the developer. These are not overloaded operators but completely new operators that don’t exist otherwise.

These operators are used within the project that we are working on. Though it is possible for us to share these operators using Swift Packages or XCFrameworks.

These operators are typically associated with a specific type and their behavior is also defined by us.

Why do we need them?

There are many reasons why we would want custom operators:

Allow for more compact and concise syntax.

Using custom operators allows our code to be more compact. Entire function calls can be condensed into a single operator.

Make the code more readable

This also improves the readability of our code. Properly chosen symbols can convey the message immediately and easily.

Allow for consistency in design of code

One of the other things that custom operators help us achieve is consistency. By using standard operations as operators we make our code more familiar and consistent to others who may read it. Programmers are familiar with the concept of operators and using them for different operations. So even if they may not immediately recognise the operator they would understand that there is some task for them to perform.

And finally it encourages reusability.

What do we need to create custom operators?

There are a couple of things that we need to create custom operators:

A logic for the action being performed by the operator
A list of valid symbols
Information about the operators attributes like prefix, postfix, infix.
The precedence of the operator if it is an infix operator

Operator Rules

There are some rules that must be followed when we are constructing the symbol for our operator. Most of the requirements are rather straightforward. However, choosing the right symbol is a very important task. There are a set of symbols that are allowed.

There are rules as far as whitespace around operators is concerned.

And finally there are certain symbols are allowed only in combination with other symbols.

Operator types

Type	Description
Prefix	Operators that appear before a variable or value. These are unary operators.
Postfix	Operators that appear after a variable or value. These are unary operators.
Infix	Operators that appear in between variables or values. These are binary operators.

Allowed Characters

This is the important bit. Which characters are allowed for usage as an operator.

We can have ASCII symbols that are used for builtin operators.

There are also many mathematical symbols that can be used as operators.

Note that the list of symbols show in the slide are not complete.

Type	Examples of different symbols
ASCII Characters	/, =, -, +, !, *, %,<, >, &, \|, ^, ?, ~
Mathematical Operators, Miscellaneous symbols, dingbats*	∝, √, ⊆, ≿, ∫

Here are some more

U+00A1–U+00A7	U+2190–U+23FF
U+00A9 or U+00AB	U+2500–U+2775
U+00AC or U+00AE	U+2794–U+2BFF
U+00B0–U+00B1	U+2E00–U+2E7F
U+00B6	U+3001–U+3003
U+00BB	U+3008–U+3020
U+00BF	U+3030
U+00D7	U+0300–U+036F
U+00F7	U+1DC0–U+1DFF
U+2016–U+2017	U+20D0–U+20FF
U+2020–U+2027	U+FE00–U+FE0F
U+2030–U+203E	U+FE20–U+FE2F
U+2041–U+2053	U+E0100–U+E01EF
U+2055–U+205E

Whitespace

The next important bit is the whitespace around the operator.

If an operator has a whitespace on both the sides or doesn’t have whitespace on both the sides then it is interpreted as a binary operator. This is what would appear for infix operator.

If an operator has whitespace only on the left then it is a prefix unary operator.

If an operator has whitespace only on the right then it is a postfix unary operator.

If an operator does not have whitespace on the left but is followed by a dot then it is treated as a postfix unary operator.

Finally, any round, brace, square brackets appearing before or after the operator along with comma, colon, & semicolon are treated as whitespace

Making sure that we put the whitespace in the correct place while using these operators is very important.

No.	Rule	Example code
1	If an operator has a whitespace on both the sides or doesn’t have whitespace on both the sides then it is interpreted as a binary operator	ab or a b
2	If an operator has whitespace only on the left then it is a prefix unary operator	**a
3	If an operator has whitespace only on the right then it is a postfix unary operator	a**
4	If an operator does not have whitespace on the left but is followed by a dot then it is treated as a postfix unary operator	a.b is treated as a .b
5	(, {, [ before the operator and ), }, ] after the operator along with ,, :, ; are treated as whitespace

There are some exceptions to the rules we just saw. Especially with exclamation mark & question mark.

! & ? which are predefined are always treated as postfix if there is no whitespace on the left
If we wish to use ? In optional chaining then it must not have whitespace on the left
To use it as a ternary conditional operator ?: it must have whitespace on both the sides
Operators with a leading or trailing <, > are split into multiple tokens. For example, in Dictionary<String, Array<Int>> the last 2 arrows are not interpreted as shift operator.

Operator grammar

There are rules for constructing operators. Only certain combinations are allowed.

Each operator contains a symbol which forms the operator head. The head is the first character in the operator.

The head may or may not be followed by 1 or more characters which are operator characters.

The head and the optional characters combined together form the operator.

The head itself can contain a one out of a set of valid symbols. Or it can contain a period.

These are some of the symbols allowed for usage as the head of the operator. You can choose any one of those.

/, =, -, +, !, *, %,<, >, &, \|, ^, ?, ~	U+2055–U+205E
U+00A1–U+00A7	U+2190–U+23FF
U+00A9 or U+00AB	U+2500–U+2775
U+00AC or U+00AE	U+2794–U+2BFF
U+00B0–U+00B1	U+2E00–U+2E7F
U+00B6	U+3001–U+3003
U+00BB	U+3008–U+3020
U+00BF	U+3030
U+00D7
U+00F7
U+2016–U+2017
U+2020–U+2027
U+2030–U+203E
U+2041–U+2053

For the successive characters you can use any of the symbols allowed for the head plus some additional allowed symbols. The list above contains all the allowed symbols.

/, =, -, +, !, *, %,<, >, &, \|, ^, ?, ~	U+2055–U+205E
U+00A1–U+00A7	U+2190–U+23FF
U+00A9 or U+00AB	U+2500–U+2775
U+00AC or U+00AE	U+2794–U+2BFF
U+00B0–U+00B1	U+2E00–U+2E7F
U+00B6	U+3001–U+3003
U+00BB	U+3008–U+3020
U+00BF	U+3030
U+00D7	U+0300–U+036F
U+00F7	U+1DC0–U+1DFF
U+2016–U+2017	U+20D0–U+20FF
U+2020–U+2027	U+FE00–U+FE0F
U+2030–U+203E	U+FE20–U+FE2F
U+2041–U+2053	U+E0100–U+E01EF

Examples

.+.
≈
√
**

Operator Precedence

As far as infix operators are concerned there is also the question of precedence. Precedence is used to determine the operator priority when there are multiple operators in a single statement.

precedencegroup <#precedence group name#> {
    higherThan: <#lower group names#>
    lowerThan: <#higher group names#>
    associativity: <#associativity#>
    assignment: <#assignment#>
}

While the first 2 values are straightforward, they simply help determine the exact position of the newly created precedence as compared to existing precedences, the associativity and assignment are extra items that are not immediately clear.

Type	Description	Values
Associativity	Determines order in which a sequence of operators with the same precedence are evaluated in the absence of grouping brackets	left, right, none
Assignment	Specifies priority when used with optional chaining. TRUE: Same grouping rules as assignment operator from standard libraryFALSE: Same rules as operators that don’t perform assignment	true, false

The assignment of a precedence group specifies the precedence of an operator when used in an operation that includes optional chaining. When set to true, an operator in the corresponding precedence group uses the same grouping rules during optional chaining as the assignment operators from the standard library. Otherwise, when set to false or omitted, operators in the precedence group follows the same optional chaining rules as operators that don’t perform assignment.

Determines order in which a sequence of operators with the same precedence are evaluated in the absence of grouping brackets. so for example 4 – 6 – 7 has the minus sign which has left associativity. The operation 4-6 is grouped and then the – 7 operation is performed.

Nonassociative operators of the same precedence level can’t appear adjacent to each to other.

The priority for the built in precedences can be seen in Apple’s documentation.

Creating the operators

It is fairly easy to create our own operators. You can try the code in a playground. We will be creating 1 operator of each type: postfix, prefix, infix.

Create a new playground.
Declare the creation of the prefix operator as shown. This will be used as a squaring operator.

prefix operator **

Now we will provide a generic version of the operator implementation.

prefix func **<T:Numeric> (inputValue : T) -> T {
    return inputValue * inputValue
}

That’s it. It is that simple to create our own prefix operator. Now let us test it.

Create a variable of type Float and use the operator we have just created.

var lengthOfSideOfSquare : Float = 1.1

var areaOfSquare : Float = **lengthOfSideOfSquare

print("The area of a square whose side is \(lengthOfSideOfSquare) centimeters long is \(areaOfSquare) square centimeters")

Similarly declare a postfix operator. This one will perform conversion to a string.

postfix operator ~>

Now we will implement this operator. To do that let us make a simple type which will have the to string operator capability.

struct Person {
    var name : String = ""
    var age : Int = 0
}

extension Person {
    static postfix func ~> (inputValue : Person) -> String {
        return "NAME: \(inputValue.name)\nAGE: \(inputValue.age)"
    }
}

Let us try this operator out and see.

var developer : Person = Person(name: "Arun Patwardhan",
                                age: 35)

var description : String = developer~>

print(#line, description)

Now let us implement an infix operator. The one that we are going to implement is a similarity operator which can be used to determine the degree of similarity between objects of the same type. To do that let us start off by declaring an enum which holds the values for the degree of similarity.

enum DegreeOfSimilarity {
    case exactly_the_same
    case almost_the_same
    case slightly_similar
    case completely_different
}

Infix operator can also have a precedence associated with it. Let us declare our own precedence and use it for our operator.

precedencegroup DegreeOfSimilarityPrecedence {
    higherThan: AdditionPrecedence
    lowerThan: MultiplicationPrecedence
    associativity: none
    assignment: true
}

Let us examine the values we have given:

higherThan: This indicates that our precedence has higher priority than the Addition precedence

lowerThan: This indicates that our precedence has lower priority than the Multiplication precedence

Associativity: This indicates that our operator is not associative. So we cannot combine multiple occurrences of our operator in one statement.

assignment: This indicates that out operators has the same behaviour, as other operators that assign, when it comes to optional chaining.

Now we can declare our infix operator.

infix operator ≈ : DegreeOfSimilarityPrecedence

It is useful to save your new operator symbols as code snippets to easily use them. You can read thi s article if you don’t know how to create a code snippet.

Let us look at the implementation. I am going to use the same person type we used earlier.

extension Person {
    static func ≈ (lhsValue : Person, rhsValue : Person) -> DegreeOfSimilarity {
        guard lhsValue.name == rhsValue.name else {
            return DegreeOfSimilarity.completely_different
        }
        
        guard lhsValue.age == rhsValue.age else {
            return DegreeOfSimilarity.almost_the_same
        }
        
        return DegreeOfSimilarity.exactly_the_same
    }
}

Now we will test them and see.

var employee1 : Person = Person(name: "Jack",
                                age: 22)

var employee2 : Person = Person(name: "John",
                                age: 21)

var employee3 : Person = Person(name: "Jack",
                                age: 23)

var employee4 : Person = Person(name: "Jack",
                                age: 23)

print(#line, employee1 ≈ employee2)

print(#line, employee1 ≈ employee3)

print(#line, employee3 ≈ employee4)

Run the code and see the end result.

Feel free to create more operators and play around. You could also package these operators in a swift package and share them around. I have shared links to

Summary the new operator

Creating operators is very easy. Most of the requirements are rather straightforward. However, choosing the right symbol is a very important task.

The one thing that we should keep in mind is not to over use these. It can be tempting to do this. But abstracting everything can make the code look a little too vague.

So that is how you can create operators.

Download the sample project

I have uploaded some of the custom operators, that I have shown above, as a Swift Package. You can download the package as well as a demo project, which shows how to use them, from the links below.

Custom Operators Swift Package Download

Custom Operators usage Demo Project Download

Video

Here is the video describing what we discussed above.

Creating Code Snippets in Xcode

September 18, 2020September 18, 2020 / Arun Patwardhan / 1 Comment

What are code snippets?

Code snippets are as the name suggests, short pieces of code that can quickly be inserted into your code file. This is done either by dragging the snippet or by typing out the completion. Code snippets are very easy to create and use and can be applied in a wide variety of situations.

We will look at how you can create & use snippets. The following example is done in a playground, but this could be done from anywhere within Xcode.

Note: The example below was performed on Xcode 11.7

How do we create code snippets?

Start off by writing the code or text that you want to convert into a snippet. For example, I have a set of comments that I add at the start of every function. Write it down.

/**
 This function performs a comparison of the 2 objects
 - important: This function does not perform data validation.
 - returns: `Bool`.
 - requires: iOS 13 or later
 - Since: iOS 13
 - parameter lhsValue: This holds the value on the lhs of the operator
 - parameter rhsValue: This holds the value on the rhs of the operator
 - Example: `var answer =  venueAddress == hotelAddress`
 - author: Arun Patwardhan
 - copyright: Copyright (c) Amaranthine 2020
 - date: 14th September 2020
 - version: 1.0
 */

2. Select it.
3. From the menu bar select Editor > Create Code Snippet.

This brings up the snippet editor.
4. Give your snippet the following details.

Option	Description
Name	This is the name of your code snippet.
Platform	This determines whether your snippet is available only for certain platforms: say only for iOS.
Availability	This determines the place where the snippet can be added.
Completion	This is the word that we will be typing in the Xcode editor to trigger the implementation of the snippet
Language	This specifies the language for which the snippet will be applied.

Name: Func Documentation

Language: Swift

Platform: All

Availability: All scopes

Completion: doc

Note that the values for Name and Completion can be whatever you want.

This is how the snippet should look.

5. Now we will try to use it in the editor. Start typing the completion word in the Xcode editor.

6. Select the snippet with your name and completion.
7. Hit enter. You should see the comments you want appearing in the editor.

Placeholder

We can make our snippet above even better by using placeholders. Placeholders are pieces of text that can be replaced by the user. They also give information about what is expected in the placeholder.

We can add place holders by simply typing the hint inside placeholder brackets. Placeholder brackets are nothing but open <# and closing #>. For example:

<# some text #>

Which appears as

The user will simply click on the “some text” placeholder.

There are plenty of places in our comments where we can use placeholders. When we use the code snippet it should put comments with place holders in them.

Let us change the comments in our Xcode editor first. We will edit the snippet later on. Make the changes as shown below.

/**
 <# put the description of your function here #>
 - important: <# mention some important points here #>
 - returns: `<# return type #>`.
 - requires: iOS  <#iOS Version#>  or later
 - Since: iOS  <#iOS Version#>
 - parameter <#param 1#>: This holds the value on the lhs of the operator
 - parameter <#param2#>: This holds the value on the rhs of the operator
 - Example: `<#put some example code here#>`
 - author: Arun Patwardhan
 - copyright: Copyright (c) Amaranthine 2020
 - date: <#day#>  <#month#>  <#year#>
 - version: 1.0
 */

We have made the following items into comments.

Description
OS Version
Return type
Important comments
Parameter 1 & 2 names
Sample code
Day, Month, & Year

Of course, there are other things we could change too. Feel free to make any other changes you can think of.

2. Let us now copy these changes to the code snippet we created. Copy the code from the Xcode editor.

To bring the snippet editor again simply click on the add object button in the upper right hand corner of Xcode.

4. Select the snippet from the list on the left and click edit.
5. Paste the code that you just copied. Your snippet editor should look like this:

6. Click on ‘Done’ once you are finished making changes. Your snippet will now be ready.

7. Try adding the snippet into your editor just like before. Simply type in the completion for your snippet.

Dragging snippets

We can use the autocompletion we saw earlier. But it is also possible for us to drag snippets.

Exporting code snippets

Once created it is possible to export/import code snippets too. All the snippets are located in the following folder.

~/Library/Developer/Xcode/UserData/CodeSnippets/

Any snippets you have created will be located there.

Any new snippets to be added will have to be added there.

Summary

Code snippets are easy to create and have several advantages:

They improve the developers experience
Promote consistent code
Speeds up the process of writing code
Encourages developers to use each others snippets and gain the first 3 advantages.

Creating and using snippets is very very easy and has a lot of benefits. So go ahead and create snippets.

Useful scripts for macOS

March 27, 2020March 27, 2020 / Arun Patwardhan / 2 Comments

Getting Started

You might find these articles useful

One of the advantages with scripts is the fact that you can easily automate many tasks. Here is an article that walks you through that process.

If you come across a situation where you want to perform a set of tasks on multiple computers then scripts come in very handy.

I will be providing the Shell Script version of the task. Feel free to make changes to the scripts as required. I will try to provide an AppleScript version of the tasks a little later.

This is not the only way to implement the scripts. There may be multiple approaches towards achieving the same result. You will have to explore and examine the correct approach.

This is not a comprehensive list. The scripts should give you some ideas and act as a useful reference when you are creating your own scripts.

I have tested these scripts on macOS Catalina 10.15

Download

You can download all the scripts from here.

Script Category	Page Number
Settings and Accounts	1
Security	2
Data	3
Information Collection	4
File System	5

Disclaimer

The Software Is Provided “As Is”, Without Warranty Of Any Kind, Express Or Implied, Including But Not Limited To The Warranties Of Merchantability, Fitness For A Particular Purpose And Noninfringement. In No Event Shall The Authors Or Copyright Holders Be Liable For Any Claim, Damages Or Other Liability, Whether In An Action Of Contract, Tort Or Otherwise, Arising From, Out Of Or In Connection With The Software Or The Use Or Other Dealings In The Software.

WARNING

Please try these scripts on a test computer. Some of the scripts do make changes to the system. Always test before using these scripts.

Pages: 1 2 3 4 5 6

Creating iOS Apps without Storyboard – Part 1

July 28, 2019August 7, 2019 / Arun Patwardhan / 2 Comments

What are “nibless” apps?

Apps which are designed without the help of Storyboard are called as “Nibless” apps. Normally we design an app with the help of a Storyboard file. Earlier they were called Xib files or Nib files. Hence the term “Nibless”.

Why should we create Apps without storyboard?

There are a number of reasons.

It makes for a better experience when implementing along with version control.
Allows us to create UI elements dynamically.
Makes reusable UI Components easier to distribute and reuse.

How can we create Apps without Storyboard?

There are a couple of things that need to be done. Firstly the Main.storyboard file needs to be removed and the project settings need to be updated to reflect this change.. We are doing this since we won’t be using the storyboard file.
Everything will now have to be started up by us manually. Many of these tasks were taken care of by storyboard, but since that was removed we will have to do it. This means we have to manually create the window, create the view controller set it as a the root view controller.
We also have to manually create each and every component on our own. That is the very thing we were trying to achieve.

This example is implemented on Xcode 10.3 on macOS 10.14.5. We are not implementing auto layout in this article. We will look at implementing that programmatically in the next article.

Let us start with an empty project. Open Xcode.
Select File > New > Project
Give it any name. Select the language as Swift & leave the checkboxes unchecked.
Once the project loads select the Main.storyboard file and delete it.
Switch to the Project settings file.
Remove the entry for the main interface.
It is a good idea to leave the LaunchScreen.storyboard file. The reason for this is to give the launch process a reference of the screen size it needs to produce. Else it will default down to the 0,0,320,480 which is the old iPhone size.
Switch to the AppDelegate.swift file.

Add the following property below the UI Window declaration.

  
let mainScreenController : ViewController = ViewController()

Add the code to create the window and set root view controller in the didFinishLaunchingWithOptions method

   
//1. Create the UIWindow object   
self.window = UIWindow(frame: UIScreen.main.bounds)   

//2. Set the root view controller   
self.window?.rootViewController = self.mainScreenController   

//3. Make the window key and visible  
self.window?.makeKeyAndVisible()

Switch to the ViewController.swift file.

Declare the following variables

  
//UI Variables  
var labelDemo   : UILabel?  
var imageDemo   : UIImageView?  
var buttonDemo  : UIButton = UIButton(type: UIButton.ButtonType.roundedRect) 
var dataField   : UITextField?

Implement the function to create labels. The process of creating a view programmatically is fairly straightforward. Barring a few variations depending on the view component nothing is drastically different.

  
func createLabel() 
{      
     //1. Specify the dimensions      
     let labelRect : CGRect   = CGRect(x: 100.0, y: 50.0, width: self.view.frame.size.width - 130.0, height: 60.0)     

     //2. Create the view object      
     labelDemo                = UILabel(frame: labelRect)      

     //3. Customise the view attributes      
     labelDemo?.text          = "This is my first Programmatic App."                
     labelDemo?.textColor     = UIColor.yellow      
     labelDemo?.textAlignment = NSTextAlignment.left  
     labelDemo?.numberOfLines = 0      
     labelDemo?.font          = UIFont.boldSystemFont(ofSize: 20.0)      

     //4. Add the view to the subview      
     self.view.addSubview(labelDemo!) 
}

Let us examine the steps one by one.

 
//1. Specify the dimensions 
let labelRect : CGRect = CGRect(x: 100.0, y: 50.0, width: self.view.frame.size.width - 130.0, height: 60.0)

This will define the dimensions of the view. As we are not implementing auto layout we will need to do this manually.

 
//2. Create the view object
labelDemo = UILabel(frame: labelRect)

Now that we have the dimensions we can go ahead and instantiate an instance of the label object using those dimensions. These 2 parts are the same as dragging a label from the object library onto the storyboard and placing it onto the storyboard per our requirements.

//3. Customise the view attributes 
labelDemo?.text          = "This is my first Programmatic App."     
labelDemo?.textColor     = UIColor.yellow 
labelDemo?.textAlignment = NSTextAlignment.center      
labelDemo?.numberOfLines = 0 
labelDemo?.font          = UIFont.boldSystemFont(ofSize: 20.0)

This part is the same as changing the attributes in the attributes inspector. This is where we customise the label.

 
//4. Add the view to the subview 
self.view.addSubview(labelDemo!)

This last part also forms one part of dragging the label on to the storyboard. When we drag a view on to the storyboard it is placed within the main view that belongs to the ViewController. This statement completes the above process.

Repeat the above steps for showing an image.

func createImage()
{
     //1. Specify the dimensions
     let imageRect  : CGRect  = CGRect(x: 30.0, y: 50.0, width: 60.0, height: 60.0)

     //2. Create the image model
     let imageModel : UIImage = UIImage(named: "logo.png")!

     //3. Create the view object
     imageDemo                = UIImageView(frame: imageRect)

     //4. Customise the view attributes
     imageDemo?.image         = imageModel
     imageDemo?.contentMode   = UIView.ContentMode.scaleAspectFit

     //5. Add the view to the subview
     self.view.addSubview(imageDemo!)
}

The code above is almost similar to the one created for labels except for the fact that we had to explicitly create a model object for the view. Images being different from strings, require this process to be done explicitly.

Similarly let us implement the code for creating buttons

func createButton()
{
     //1. Specify the dimensions
     let buttonRect : CGRect = CGRect(x: 30.0, y: 220.0, width: 100.0, height: 50.0)

     //2. Provide the frame to the button
     buttonDemo.frame = buttonRect

     //3. Customise the view attributes
     buttonDemo.setTitle("Click Me", for: UIControl.State.normal)
     buttonDemo.addTarget(self, action: #selector(ViewController.clickMeTapped), for: UIControl.Event.touchDown)

     //4. Add the view to the subview
     self.view.addSubview(buttonDemo)
}

@objc func clickMeTapped(
{
     print("Click me tapped!")
}

Again just minor variations here. Mainly the step to add a target function to be invoked when the button is tapped. We also need to write the target function itself.

We will also implement the code to create a text field.

func createTextField()
{
    //1. Provide dimensions for the view
    let tfRect : CGRect             = CGRect(x: 30.0, y: 140.0, width: self.view.frame.size.width - 60.0, height: 50.0)
        
    //2. Create the view object
    dataField                       = UITextField(frame: tfRect)
        
    //3. Customise the attributes of the view
    dataField?.placeholder          = "Enter Name"
    dataField?.borderStyle          = UITextField.BorderStyle.roundedRect
    dataField?.keyboardType         = UIKeyboardType.namePhonePad
    dataField?.keyboardAppearance   = UIKeyboardAppearance.dark
    dataField?.returnKeyType        = UIReturnKeyType.go
        
    //4. Add the view to the subview
    self.view.addSubview(dataField!)
}

Next we need to call all these functions. I have implemented a single creator function for that.

func createUIElements()
{
     self.createLabel()
     self.createImage()
     self.createButton()
     self.createTextField()
}

Lastly we will call this function in the viewDidLoad method. Add the following lines to the viewDidLoad method.
```
self.view.backgroundColor = UIColor.lightGray
self.createUIElements()
```
I have also added code to change the background colour so that we can see the background clearly.
Run the project. Everything should appear normally.

Are there any benefits of creating apps without storyboard?

The points mentioned in the “why should we make programmatic apps?” section are some of the advantages. Beyond that there aren’t too many.
If you are looking at a team based project development then this approach is good.
There is no difference in terms of memory or performance when it comes down to apps design with or without storyboard.

Are there any drawbacks?

As can be seen from the example above, there are a couple of drawbacks

The main drawback is that you can’t get a quick preview of how your app looks. You have to run the simulation every time you wish to see the end result.
There is a lot more coding involved. Which can be daunting to those who are overly accustomed to designing with the help of storyboards

Note

A small point. I have left the LaunchScreen.storyboard file. I did not delete it. The reason I did that was to allow the app to allow the system to determine the dimensions on the device. If we do delete the file then the UIScreen.main.bounds return (0.0, 0.0, 320.0, 480.0) which are the old iPhone screen size settings.
While you can go ahead and make changes programmatically it is a lot easier to just leave the LaunchScreen.storyboard file there.

Carrying on from the previous point. It actually is okay if you leave the Main.storyboard file as is too. In which case you will have to skip steps 5,6,8,9,10. The code is still running programmatically but you do not have to create the main ViewController manually.

Download the Source Code

You can download the Xcode Project from this link.

Creating reusable UI Components for iOS App Development

December 8, 2018December 19, 2018 / Arun Patwardhan / Leave a comment

In an earlier article I had discussed how we can create our own frameworks to easily share reusable code. In this article we will take this a little further and create our own reusable UI Components.

Points to Note:

The reusable component we will be creating is based on UIKit. For that reason this component can only be used in iOS Apps. However, you can follow the same steps to create a reusable component for macOS using Cocoa.
UI Components, distributed through a framework, do not render in the project storyboard file.
You should be familiar with creating Embedded Binaries (your own Framework). If you aren’t then please read this article first.
These projects are created on Xcode 10 with Swift 4.2

Getting Started

We will complete the implementation as a 2 step process. Here is the screen that we are planning to implement.

Creating the Reusable Framework

Open Xcode and create a new Framework project.
Name the project “UIVIdentityCard”.
Save the project in any folder.
Create a new Swift file File > New > File > Swift.
Name the file “GenderType.swift”. This is where we will declare the enum that holds the Gender type that we are creating.

Add the following code to the file.

 
import Foundation 
/** Possible scores that can be given. 
*values* 
`Male` 

`Female` 

`NotSpecified` 

*functions* 
`func toString() -> String` 
Used to get the `String` version of the value 

- Author: Arun Patwardhan 
- Version: 1.0 
*/ 
public enum GenderType 
{      
     case Male      
     case Female      
     case NotSpecified 
} 

/** This extension adds the Enum to String converions capability 
- Author: Arun Patwardhan 
- Version: 1.1 
*/ 
extension GenderType 
{      
     /** This function converts from enum value to `String`         
     - important: This function does not do validation         
     - returns: `String`.         
     - requires: iOS 11 or later         
     - Since: iOS 11         
     - author: Arun Patwardhan         
     - copyright: Copyright (c) Amaranthine 2015         
     - version: 1.0 */      
     @available(iOS, introduced: 11.0, message: "convert to String")      
     func toString() -> String      
     {           
          switch self           
          {                
               case .Male:                     
                    return "Male"                
               case .Female:                     
                    return "Female"                
               case .NotSpecified:                     
                    return "Not Specified"           
          }      
     } 
}

Create a new Swift file called “PersonDetailsModel.swift”.

Add the following code to the file.

import Foundation

/**  This struct represents the data that is to be shown in the ID card  
**Variables**  
`personName`  

`personIcon`  

`personDob`  
Date of Birth  

`personAddress` 
 
`personPhone` 
 
`personEmail` 
 
`personCompany`
  
`personHeight`
  
`personWeight`  

`personGender`  

**Important**  There is a variable with the name `entryCount`. This variable keeps tracks of the number of stored properties that exist. The value of this variable will be used to determine the number of rows in the table.The computed property `numberOfRows` is the property used to access the value of `entryCount`.  

- Author: Arun Patwardhan  
- Version: 1.0
*/
public struct PersonDetailsModel
{     
     internal var entryCount : Int = 7     
     public var personName   : String = ""     
     public var personIcon   : UIImage     
     public var personDob    : Date     
     public var personAddress: String = ""     
     public var personPhone  : String = ""     
     public var personEmail  : String = ""     
     public var personCompany: String = ""     
     public var personHeight : Double? = 0.0     
     {          
          willSet          
          {               
               if newValue == nil & personHeight != nil               
               {                    
                    entryCount -= 1               
               }               
               else if newValue != nil & personHeight == nil               
               {                    
                    entryCount += 1               
               }          
          }     
     }     

     public var personWeight : Double? = 0.0     
     {          
          willSet(newValue)          
          {               
               if newValue == nil & personWeight != nil               
               {                    
                    entryCount -= 1               
               }               
               else if newValue != nil & personWeight == nil               
               {                    
                    entryCount += 1               
               }          
          }     
     }     

     public var personGender : GenderType?     
     {          
          willSet          
          {               
               if newValue == nil & personGender != nil               
               {                    
                    entryCount -= 1               
               }               
               else if newValue != nil & personGender == nil               
               {                    
                    entryCount += 1               
               }          
          }     
     }     

     public var numberOfRows : Int     
     {          
          return entryCount     
     }     

     public init(withName newName : String, icon newIcon : UIImage, birthday newDob : Date, address newAddress : String, phone newPhone : String, email newEmail : String, Company newCompany : String, height newHeight : Double?, weight newWeight : Double?, andGender newGender : GenderType?)     
     {          
          personName = newName          
          personIcon = newIcon          
          personDob  = newDob          
          personAddress = newAddress          
          personPhone = newPhone          
          personEmail = newEmail          
          personCompany = newCompany  
        
          if newGender != nil          
          {               
               entryCount += 1          
          }          
          if newWeight != nil          
          {               
               entryCount += 1          
          }          
          if newHeight != nil          
          {               
               entryCount += 1          
          }          

          personHeight = newHeight          
          personWeight = newWeight          
          personGender = newGender     
     }
}

/**     This extension adds protocol conformance for the `CustomStringConvertible` protocol.     

- Author: Arun Patwardhan     
- Version: 1.1
*/
extension PersonDetailsModel : CustomStringConvertible
{     
     public var description: String     
     {          
          return """               
               NAME: \(self.personName)               
               DATE OF BIRTH:\(self.personDob)               
               ADDRESS: \(self.personAddress)               
               EMAIL:\(self.personEmail)               
               PHONE:\(self.personPhone)          
          """     
     }
}

Now we will focus out attention on the View. Create a new file File > New > File > View.
Name the view “UIVIdentityCard.swift”.
Design the view as shown in the screenshot below.
Create the corresponding“UIVIdentityCard.swift” file.
Make the IBOutlet & IBAction connections for the different UI elements.

Add the following code. This is how your file should look after its completed.

/**     The UIVIdentityCard class     
**Functions**     
`public func load(data newPerson : PersonDetailsModel)`     
Used to load the data for the view.     

- Author: Arun Patwardhan     
- Version: 1.0
*/
@IBDesignableopen class UIVIdentityCard: UIView, UITableViewDelegate, UITableViewDataSource
{     
     //IBOutlets --------------------------------------------------     
     @IBOutlet public weak var personIcon : UIImageView!     
     @IBOutlet public weak var personName : UILabel!     
     @IBOutlet public weak var personDetails : UITableView! 

     //Variables --------------------------------------------------     
     public var localTableData : PersonDetailsModel!     
     let nibName : String = "UIVIdentityCard"     
     var view: UIView!     
     let cellIdentifier : String = "IDCard"     
     //Functions --------------------------------------------------     
     /**     This function does the initial setup of the view. There are multiple things happening in this file.     
     1) The first thing that we do is to load the Nib file using the `nibName` we saved above. The UNIb object contains all the elements we have within the Nib file. The UINib object loads the object graph in memory but does not unarchive them. To unarchive them and get the ibjects loaded completely for use we have to instatiate the object and get the arry of top level objects. We are however interested in the first object that is there in the array which is of type `UIView`. The reference to this view is assigned to our local `view` variable.     
     2) Next we specify the bounds of our view     
     3) Finally we add this view as a subview     

     - important: This function does not do validation     
     - requires: iOS 11 or later, the varibale that contains the name of the nib file.     
     - Since: iOS 11     
     - author: Arun Patwardhan     
     - copyright: Copyright (c) Amaranthine 2015     
     - version: 1.0     
     */     
     @available(iOS, introduced: 11.0, message: "setup view")     
     func setup()     
     {          
          //1)          
          self.view = UINib(nibName: self.nibName, bundle: Bundle(for: type(of: self))).instantiate(withOwner: self, options: nil)[0] as! UIView          
     
          //2)          
          self.view.frame = bounds          
          
          //3)          
          self.addSubview(self.view)     
     }     

     public func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int     
     {          
          if let count = localTableData?.entryCount          
          {               
               return count - 2          
          }          
          return 0     
     }     

     public func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -&amp;gt; UITableViewCell     
     {          
          var cell : UITableViewCell? = tableView.dequeueReusableCell(withIdentifier: cellIdentifier)          

          if nil == cell          
          {               
               cell = UITableViewCell(style: .default, reuseIdentifier: cellIdentifier)          
          }          

          switch indexPath.row          
          {               
               case 0:                    
                    let formatter = DateFormatter()                    
                    formatter.dateStyle = .medium                         
                    cell?.textLabel?.text = "Birthday\t: "+ formatter.string(from: (localTableData?.personDob)!)      

               case 1:                    
                    cell?.textLabel?.text = "Email\t: " + localTableData.personEmail               

               case 2:                    
                    cell?.textLabel?.text = "Phone\t: " + localTableData.personPhone               

               case 3:                    
                    cell?.textLabel?.text = "Address\t: " + localTableData.personAddress               

               case 4:                    cell?.textLabel?.text = "Company\t: " + localTableData.personCompany               

               case 5:                    
                    cell?.textLabel?.text = "Gender\t: " + \(localTableData.personGender?.toString())!               

               case 6:                    
                    cell?.textLabel?.text = "Height\t: \((localTableData.personHeight)!)"               

               case 7:                    
                    cell?.textLabel?.text = "Weight\t: \((localTableData.personWeight)!)"               
               default:                    
                    print("error")          
          }          

          cell?.textLabel?.font = UIFont.boldSystemFont(ofSize: 12.0)          
          cell?.textLabel?.setContentCompressionResistancePriority(.defaultHigh, for: .horizontal)          
          return cell!     
     }     

     //Inits --------------------------------------------------                    
     override public init(frame: CGRect)     
     {          
          super.init(frame: frame)          
          self.setup()     
     }     
     
     required public init?(coder aDecoder: NSCoder)     
     {          
          super.init(coder: aDecoder)          
          self.setup()     
     }     

     override open func layoutSubviews()     
     {          
     super.layoutSubviews()     
     }
}

/**     This extension adds the function to load data     
- Author: Arun Patwardhan     
- Version: 1.1
*/
extension UIVIdentityCard
{     
     /**          
     This function loads the data for the view          
     - important: This function does not do validation          
     - parameter newPerson: This is the object representing the person whose information will be displayed on the screen.          
     - requires: iOS 11 or later          
     - Since: iOS 11          
     - author: Arun Patwardhan          
     - copyright: Copyright (c) Amaranthine 2015          
     - version: 1.0     
     */    
     @available(iOS, introduced: 11.0, message: "load data")     
     public func load(data newPerson : PersonDetailsModel)     
     {          
          self.localTableData = newPerson          
          self.personIcon.image = localTableData.personIcon          
          self.personName.text = localTableData.personName          
          self.personDetails.reloadData()     
     }
}

Add the placeholder image for the image view.
Select any of the simulators from the list.
Press ⌘ + B to build the project.
From the Project navigator select the Framework file.
Control click and select “Show in Finder”.
Copy the framework to the “Desktop”.

We are done creating the reusable framework. We will not shift our focus towards testing this framework.

Using the Framework in a project

Let us now test the framework we created. We will do this by incorporating the code in our iOS App.

Create a new project. Call it “IdentityCardTest”.
Save the file in a folder of your choice.
Select the Project file and Embed the Framework into your project.
Add an image to your project, this will be the image that will be displayed in your custom view.
Switch to the Main.storyboard file. Drag a UIView into the ViewControllers view.
Set its identity to the UIVIdentityCard in the identity inspector. Also set its module to UIVIdentityCard.
Create an IBOutlet for this custom view.
Switch to the ViewController.swift file. Import the UIVIdentityCard framework at the top of the file.

Add the following code to the file. We will be creating test data and displaying it on the screen using the Custom view we just designed.

//Functions --------------------------------------------------
/**
    This function prepares and loads the data that is to be shown in the custom view


    - important: This function does not do validation
    - requires: iOS 11 or later, the UIVIdentityCard framework.
    - Since: iOS 11
    - author: Arun Patwardhan
    - copyright: Copyright (c) Amaranthine 2015
    - version: 1.0
*/
@available(iOS, introduced: 11.0, message: "prepares data to be shown on the ID card")
func prepareIDCard()
{
     let displayData : PersonDetailsModel = PersonDetailsModel(withName: "Arun Patwardhan", icon: UIImage(named: "iconHolder.png")!, birthday: Date(timeIntervalSince1970: 44_97_12_000), address: "Mumbai, Maharashtra, India", phone: "91-22-26486461", email: "arun@amaranthine.co.in", Company: "Amaranthine", height: 5.11, weight: nil, andGender: GenderType.Male)

     myIDCard.load(data: displayData)
}

Your completed ViewController.swift should look like this.
Run the project. See if the view loads the way we wish.

Link to Sample Code

https://github.com/AmaranthineTech/ReusuableUIFramework

Video

Creating Reusable UI

Programming Style Guide: Command Query Separation

July 20, 2018 / Arun Patwardhan / 1 Comment

An important aspect of programming, and one that people don’t think of to often, is being able to express the intentions of the code clearly.

Most of the times we programmers get lost in the code we write. It is important to step back and take a look at the code we have written from another person’s perspective. One can say, “But that’s what documentation is supposed to do right? Provide information to others!”. Yes, but that’s not the only way. A good example of that is a situation we often face with functions.

Command Query Separation

Most functions can be generalised into 2 categories.

Command Functions

Functions that act on instructions sent to it and make changes to the underlying data/model. These are commands given to a function and the callee is not expecting a response.

Query Functions

Functions that are used as queries to examine the underlying data/model. The callee is most certainly expecting a response. The function should not modify the underlying model in any way.

It is not common to find a function that does both. In fact, to be consistent command functions must never return a response and a query function must only return a response. This is how ideal separation happens. This way programmers can easily distinguish between Commands & Queries and the objective of the function becomes clear.

The real world however is quite different. Most functions we write are not guaranteed to work the way we want. The likelyhood of an error occurring while a function is being run is very high. This can happen during data validation or some underlying process. Hence, most functions are very likely to return a response indicating the success of a function. This is done using a variety of techniques. It is this feature that throws Command Query Separation for a toss.

In this article we are going to look at some ways in which we can achieve Command Query Separation while still retaining error handling capabilities.

Let us start by looking at the example written below.

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
Returns: Value of type double. The result of the division is returned. If the denominator is 0 the function returns 0
*/
double division(const double &firstNumber, const double &secondNumber)
{
     if (!floating_point_equality(firstNumber, secondNumber))
     {
          return firstNumber / secondNumber;
     }
     return 0.0;
}

The function is a rather simple implementation of division written in C++. It is meant to be a Query function. It immediately becomes clear that we are trying to do 2 things here:

We are trying to perform a division
We are trying to check if the division succeeded with the help of a return value

The problem is the fact that the function returns error codes and the result the same way. Any programmer using this function will have to write the code to distinguish between the two.

In this case the error is represented by the value ‘0’. There is no way for the caller to tell if the result of the division was 0 or if there was an error. It gets even worse if the function is a pure command function. A pure command function ideally should not return anything. However we will have to return a value to account for errors.

Here is an example of a Command Function:

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
Returns: An error code in the form of an integer. A '0' indicates success. '-1' indicates division by Zero error.
*/
int display_division_of_numbers(const double &amp;firstNumber, const double &amp;secondNumber)
{
     if (!floating_point_equality(secondNumber, ZERO))
     {
          std::cout&lt;&lt;firstNumber&lt;&lt;&quot; divided by &quot;&lt;&lt;secondNumber&lt;&lt;&quot; = &quot;&lt;&lt;(firstNumber / secondNumber)&lt;<span id="mce_SELREST_start" style="overflow:hidden;line-height:0;"></span>&lt;std::endl;
          return 0;
     }
     else
     {
          return -1;
     }
}

As we can see the function is a command function. It shouldn't be returning a value. But we are forced to return a value to communicate success.

Let us look at some alternatives.

Returning Error Codes

This approach is the one that was implemented above & has the obvious short comings.

Passing An Error Code variable

This is the next best approach. Instead of returning an error code pass in an object that represents error. After the call is completed, check to see if the error object is nil/NULL. This ensures that the return value always corresponds to an answer and nothing else.

//Potential Error Codes

typedef enum ErrorCodes
{
DIVIDE_BY_ZERO, NaN, NEGATIVE_NUMBER
} ErrorCodes;

//ErrorCode struct. This is the object that contains error information
typedef struct ErrorCode
{
public:
     ErrorCode(const ErrorCodes &code, const std::string &description)
     :errCode(code), errDescription(description)
     {

     }

     std::string description() const
     {
          return errDescription;
     }

private:
     //Holds the code
     ErrorCodes errCode;

     //holds additional information
     std::string errDescription;
} ErrorCode;

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
Argument 3: Holds a pointer to the error code object. If the object is nil then there was no error.
Returns: Value of type double. The result of the division is returned.
*/

double division_of_numbers(const double &firstNumber, const double &secondNumber, ErrorCode **error)
{
     if (!floating_point_equality(secondNumber, ZERO))
     {
          return firstNumber / secondNumber;
     }
     else
     {
          *error = new ErrorCode(DIVIDE_BY_ZERO, "Attempting to divide by zero");
     }
     return 0.0;
}

As is obvious from the code above, the return value always corresponds to the answer of the computation. All we have to do is check the ErrorCode pointer to see if it is NULL.

Here is the implementation for the Command Function.

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
Argument 3: Holds a pointer to the error code object. If the object is nil then there was no error.
*/
void display_division_of_numbers(const double &firstNumber, const double &secondNumber, ErrorCode **err = NULL)
{
if (!floating_point_equality(secondNumber, ZERO))
{
std::cout<<firstNumber<<" divided by "<<secondNumber<<" = "<<(firstNumber / secondNumber)<<std::endl;
}
else
{
*err = new ErrorCode(DIVIDE_BY_ZERO, "Attempting to divide by Zero.");
}
}

As you can see the function looks like a true Command Function. There is no value being returned. However, the caller still has to check if the Error object is NULL.

Another implementation of this is to use a complex response.

//Potential Error Codes
typedef enum ErrorCodes
{
     DIVIDE_BY_ZERO, NaN, NEGATIVE_NUMBER, NO_ERROR
} ErrorCodes;

//Response struct. It will hold either the error or a response.
typedef struct Response
{
public:
     Response(ErrorCodes err)
     : errCode(err), value(0.0)
     {

     }

     Response(double answer)
     : errCode(NO_ERROR), value(answer)
     {

     }

     ErrorCodes getError() const
     {
          return errCode;
     }

     double getValue() const
     {
          if (NO_ERROR == errCode)
          {
               return value;
          }
          return 0.0;
     }

private:
     ErrorCodes errCode;
     double value;
} Response;

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
Returns: A struct of type Response that either contains the value or the error. The caller must examine the struct before probing the value.
*/
Response* division_of_numbers(const double &firstNumber, const double &secondNumber)
{
     if (!floating_point_equality(secondNumber, ZERO))
     {
          Response *answer = new Response(firstNumber/secondNumber);
          return answer;
     }
     else
     {
          Response *error = new Response(DIVIDE_BY_ZERO);
          return error;
     }
}

This approach is a combination of the first 2 approaches. It immediately sends information to the caller that he/she must examine the object for errors before probing for the value. In the earlier example, there is no guarantee that the caller will examine the error. There is no guarantee with this approach either. But at least it simplifies the implementation for the caller and provides an easier mechanism to handle errors without having to manually create error objects.

Something similar is achieved in Swift using Associated Enums.


//Response Enum. It will hold either the error or a response.

enum Response
{
     case Error(String)
     case Value(Double)
}

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
Returns: An Enum Response that either contains the value or the error. The caller must examine the struct before probing the value.
*/

func division_of_numbers(firstNumber : Double, by secondNumber : Double) -> Response
{
     if (!floating_point_equality(firstNumber : secondNumber, Equals: ZERO))
     {
          let answer : Response = Response.Value(firstNumber/secondNumber)
          return answer;
     }
     else
     {
          let error : Response = Response.Error("Dividing by Zero")
          return error;
     }
}

Of course the Swift implementation does not need a struct as enums allow us to encapsulate a value in them.

Exceptions & Exception Handling

This is a much better approach. The idea is that you write you function to work as it is normally supposed to. If something goes wrong throw an exception. This approach completely eliminates the need to examine the return value or check to see if there are errors in the response object.

In exception based programming, your code will follow the correct path if there is no problem. If an issue occurs then your code jumps to the part where the error needs to be handled.

Here is an example:

#ifndef MathException_hpp
#define MathException_hpp

#include
#include
#include 

namespace MathematicalExceptions {
     class MathException : public std::exception
     {
          public:
               virtual const char * what() const throw ();
               MathException(const std::string &information);

          private:
               std::string description;
     };
}
#endif /* MathException_hpp */

The next file:

#include "MathException.hpp"

const char * MathematicalExceptions::MathException::what() const throw ()
{
     return description.c_str();
}

MathematicalExceptions::MathException::MathException(const std::string &information)
: description(information)
{

}

the next file.

#include <span id="mce_SELREST_start" style="overflow:hidden;line-height:0;"></span>
#include
#include "MathException.hpp"

const double ZERO = 0.0;

//Floating point equality checker
/*
Argument 1: Holds the LHS value of type double
Argument 2: Holds the RHS value of type double
Returns: Boolean value
*/
bool floating_point_equality(const double &amp;firstNumber, const double &amp;secondNumber)
{
     return fabs(firstNumber - secondNumber) &lt; std::numeric_limits::epsilon();
}

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
Returns: A struct of type Response that contains the value.
This function throws an exception of type MathematicalExceptions::MathException
*/
double division_of_numbers(const double &amp;firstNumber, const double &amp;secondNumber)
{
     if (!floating_point_equality(secondNumber, ZERO))
     {
          double answer = firstNumber / secondNumber;
          return answer;
     }
     else
     {
          MathematicalExpections::MathException exception = MathematicalExceptions::MathException(&quot;Attempting to divide by zero&quot;);
          throw exception;
     }
}

int main(int argc, const char * argv[]) {
     double numerator = 32.1;
     double denominator = 0.0;
     double answer = 0.0;

     try
     {
          answer = division_of_numbers(numerator, denominator);
     }
     catch (MathematicalExceptions::MathException &amp;err)
     {
          std::cout&lt;&lt;err.what()&lt;&lt;std::endl;
     }
     return 0;
}

Exceptions are about the closest we can come to achieving Command Query Separation. Anyone using functions that implement the Exception throwing and handling capability is clear as to whether it is a Command function or a query function without compromising on safety and error handling in any way.

Here is an example with Swift.

//Exception Enum. Will be used to throw an exception for mathematical operations
enum MathExceptions : Error
{
     case Divide_by_Zero(String)
     case NaN(String)
     case NegativeNumber(String)
}

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
Returns: The value of type Double. The caller must handle any exceptions that might be thrown.
*/
func division_of_numbers(firstNumber : Double, by secondNumber : Double) throws -> Double
{
     if (!floating_point_equality(firstNumber : secondNumber, Equals: ZERO))
     {
          let answer : Double = firstNumber / secondNumber
          return answer;
     }
     else
     {
          throw MathExceptions.Divide_by_Zero("Attempting to Divide by zero.")
     }
}

let ans : Double = 0.0

do
{
     ans = try division_of_numbers(firstNumber: 22.3, by: 0.0)
}
catch let err
{
     print(err.localizedDescription)
}

Again, the Swift implementation is rather Straightforward thanks to Associated Enums which conform to the Error protocol.

Here is how the Command function would look with exceptions.

//Division function
/*
Argument 1: Holds the numerator of type double
Argument 2: Holds the denominator of type double
*/
void display_division_of_numbers(const double &amp;firstNumber, const double &amp;secondNumber)
{
     if (!floating_point_equality(secondNumber, ZERO))
     {
          std::cout&lt;&lt;firstNumber&lt;&lt;&quot; divided by &quot;&lt;&lt;secondNumber&lt;&lt;&quot; = &quot;&lt;&lt;(firstNumber / secondNumber)&lt;<span id="mce_SELREST_start" style="overflow:hidden;line-height:0;">&#65279;</span>&lt;std::endl;
     }
     else
     {
          MathematicalExceptions::MathException exception = MathematicalExpections::MathException(&quot;Attempting to divide by zero&quot;);
          throw exception;
     }
}

This produces a much better implementation of the function, while maintaining the error handling capabilities.

Conclusion

As we can see implementing perfect Command Query Separation is not easy. But by writing our functions properly and by using better error handling such as exceptions it becomes a lot easier to achieve that. Programmers should be able to look at a function & tell if it is a ‘Command’ or a ‘Query’ knowing that error handling is not part of the function signature in any way.

Migrating to Swift from Objective-C

July 16, 2018 / Arun Patwardhan / Leave a comment

This article explores some of the advantages and challenges faced by developers while migrating to Swift from Objective-C.

1. Do we want to migrate?

Before you start the migration process remove the old adage:

If it isn’t broken, don’t fix it!

Start by identifying the reasons why you wish to migrate. Here are some possible reasons why.

The code is old and not updated for a very long time. You now wish to add new features.
The frameworks/libraries you are using in your project have upgraded to modern Swift and no longer support your old Objective-C syntax. *You may still want to just update to modern Objective-C, but this would be a good time to jump onto swift.
You see potential for improvement in code size/speed/performance by using new Swift features not available in Objective-C. For example: Generic Programming.
The developers who developed the app in Objective-C have left and the new employees are proficient at Swift. *Again not a strong reason, but a valid reason if there is no other alternative. Asking people to sit down and learn Objective-C may not be practical, especially if they don’t have a background in C Programming.
The app is due for a performance, stability, & bug fix update. This is a good time to consider migration to Swift.

Factors to keep in mind before considering migration.

The cost of migration. This is the cost of keeping a certain number of developers occupied in migrating the code. The cost is in terms of time as well as money.
Potential risks. Any change to the code increases the risk of bugs. The chances of introducing limits on backward compatibility also increase.
Benefits gained. An assessment needs to be done as to whether there are any benefits of migrating to Swift. The Return on Investment needs to be figured out.
Compatibility with 3rd Party or in house libraries that you might use.

After having thought through all this you are ready for the next step: “Prepare to Migrate”

2. Preparing to Migrate

This is where you actually begin to work on the migration of the App.

As a first step perform a full code review of the app.
The next step is a major decision. Should you rebuild your entire app from scratch or do a piece by piece migration. We will explore the advantages a little later in the article.
Look for Swift versions of 3rd frameworks/libraries you use. This is not strictly required, however, this is a good time to check for new APIs.
Identify parts of the project to migrate. This is to be done if it is a piecemeal migration. This marks you as ready for the next step: “Starting the Migration”.

3. Starting the Migration

Once you have everything in place you are ready to begin.

Migrations happen class by class. Select an Objective-C class to migrate and start working on converting it to Swift.

If you have any pure C functions then you can either choose to make them work with Swift or rewrite them in Swift.

While migrating pay special attention to your code. Here are some conversions that you can make.

See if you can make it simpler by using Generic Programming instead of usingVoid *
Replace the use of NSError * with exceptions.
Use extensions to give types new capabilities.
Consider creating your own Data structures. You may use Swift Arrays, Dictionaries if you wish. But this might be a good time to improve performance by building your own data structures.
Embrace closures and protocols a lot more.
Make extensive use of the @available attribute to describe your changes and mark availability
Start incorporating Swift Markup to make the comments from your Objective-C code more readable.
Enums pulled in from Objective-C can be made more powerful in Swift by adding methods which work with enums as a part of the enum itself.
Use property observers to make code more reactive. In some situations this might be easier than setting observers.

Migration Steps

Here are some general steps you can follow. The steps below are for both a full app conversion or a piece meal conversion.

Note: The steps mentioned below are sample steps and not necessarily the only way to achieve this.

If its a full app conversion then create a new project. Else duplicate the existing project.
Start by looking for the frameworks you need and importing them in the necessary Swift files.
Identify class(es) that you have in your Objective-C project. Start by creating empty versions of those in your Swift project. It is very likely that you may not need all the classes as you might be optimising or reworking your App’s architecture. Also it is possible that you may need new classes.
Next identify data structures used in the class. Either convert them to their swift equivalents or explore other options.
Migrate the functions directly associated with the data structures.
Migrate the variables used in the Objective-C class.
Lastly migrate the remaining functions to Swift.
Do this till you have converted all the classes that you wish to convert.

One point left to talk about is testing. Thoroughly test you app after each step you complete. If you are using XCTests, migrate a single Unit test at a time. Corresponding to the changes that you have made above.

5. Things to watch out for

There are many things to keep in mind while migrating your code.

In a mixed language project (Swift and Objective-C) Swift only features won’t be supported. So Generic Programming cannot be implemented.
Blind copying of the code from Objective-C to Swift may not result in the best output. Try to examine each line for potential optimisation opportunities.
Watch out for OS version compatibility. You may have to choose your Swift version accordingly.

6. Full Conversion versus Part by Part Conversion

Full Conversion

PROS:

The advantage of building the app from scratch is that your overall development time is less as different parts of the app can be refactored at development time.
You also have the advantage of adopting new development approaches or architectures such as Model View View Model (MVVM) or Test Driven Development (TDD).
You are in a better position to take advantage of all the Swift features as there won’t be any challenges with compatibility.
The advantages of Swift viz: Speed, Safety, and compact code are more easily achieved
If you want to support older versions of iOS then having a pure Swift and pure Objective-C version helps.

CONS:

Of course this means that your development time is large.
There is a potential for writing duplicate code in Swift especially if it is being reused in Objective-C projects. You may end up with 2 code bases for the same feature.

Part Conversion

PROS:

The advantage of migrating parts of your app is that you can split the migration over a larger period and use your resources on other projects.
In terms of cost this is less expensive and more resource friendly
The potential for duplicate code is reduced

CONS:

But on the flip side every time you take a new part to migrate you will have to make changes to the Swift code written earlier. This increases the development time and may affect the quality of the app in the long run.
You cannot take advantages of all the Swift features.
There is a chance that once the migration is complete the App may have to undergo an overhaul to take advantage of the Swift features & improve on Speed, Safety & Size.

This article just talks about some of the advantages and challenges with Migration to Swift. There are multiple approaches available and you will have to pick and choose the approach based on your needs or situation. I had written an article some time back about choosing between Swift & Objective-C, you can have a look at that too. Here is an article, for your reference, written by Apple on Migrating to Swift. Good luck & Happy Programming! Do feel free to share your experience migrating to Swift.

Using Swift Package Manager

April 9, 2018 / Arun Patwardhan / Leave a comment

About Swift Package Manager

The Swift Package Manager is the tool used to build Applications and Libraries. it streamlines the process of managing multiple Modules & Packages. Before we go ahead and learn to use Swift Package Manager we need to get familiar with some basic terminology.

Modules

Modules are used to specify a namespace and used to control access to that particular piece of code. Everything in Swift is organised as a module. An entire app can fit into a module or an app can be made using multiple modules. The fact that we can build modules using other modules means that reusing code becomes a lot easier. So, when we make an iOS App with Xcode and Swift. The entire app is considered a single module.

Targets

Targets are the end product that we want to make. So an app for iOS is a separate target. A library is a target. An app for macOS is a separate target. You can have many targets. Some can be for testing purposes only.

Packages

Packages group the necessary source files together. A package can contain more than one target. Normally one would create a package for a family of products. For example: you want to make a photo editing app that runs on macOS & iOS. You would create one package for it. That package would have 2 targets: an iOS App & a macOS App.

Products

This is a categorisation of your packages. There are 2 types of products. Executables or Libraries. A library contains the module which can be reused elsewhere. Executables are application that run & may make use of other modules.

Dependencies

Dependencies are the modules or the pieces of code that are required to make the different targets within the package. These are normally provided as URLs.

End Products

*NOTE: Before you get started you must be familiar with Setting up Swift on Linux. If you haven’t done that then please go through the updated article: UPDATE: Swift on Linux. This also makes use of Swift Package Manager.

Example

So let us get started with an example. We are going to learn how to create:

a library package called ErrorTypes
a library package, called MathOperations, that uses the ErrorTypes library package
an executable package called Calc that makes use of the MathOperations package.

We will see how to create all three elements. Also I have uploaded the ErrorTypes & MathOperations packages to the http://www.github.com repository to demonstrate the use of dependencies. You can also create your own local git repositories if you wish.

To illustrate the folder hierarchy: I have created a folder called “Developer” in my Ubuntu linux home folder. Within that I have created a folder called “SPMDEMO“. All the paths that I will be using will be with reference to these folders. You should see a structure like this:

/home/admin/Developer/SPMDEMO/ErrorTypes
/home/admin/Developer/SPMDEMO/MathOperations
/home/admin/Developer/SPMDEMO/Calc

You are free to follow this exercise using your own folder locations. Just modify the paths accordingly.

swift package init
swift package init --type executable
swift build

If you need help with the commands run:

swift package --help
swift --help

Creating a Package

First let us start off by creating the ErrorTypes package.
```
mkdir ErrorTypes
```
Navigate to the folder and create the package:
```
cd ErrorTypes
swift package init
```
By default init will create a library package type.
Navigate to the folder containing the source files:
```
cd ./Sources/ErrorTypes/
```

Open the ErrorTypes.swift file and write the following code

public enum ErrorCodes : Error
{
     case FileNotFound(String)
     case DivideByZero(String)
     case UnknownError(String)
}

public struct MathConstants
{
     static let pi : Float = 3.14159
     static let e  : Float = 2.68791
}

Feel free to add some code of your own. The above is just an example.

Run the command to build to make sure that there aren’t any issues. You shouldn’t have any as there are no dependencies of any kind. Its a simple straightforward piece of code.
```
swift build
```
If everything is fine check your code into a git repository. This can be local or on the web. Remember that we will need the URL to this repository.
Navigate back to the SPMDEMO folder.
```
cd ~/Developer/SPMDEMO/
```
Create a folder called MathOperations.
```
mkdir MathOperations
```
Navigate to the newly created folder and run the command to create a library package.
```
cd MathOperations
swift package init
```
Navigate to the sources folder:
```
cd ./Sources/MathOperations/
```

Open the MathOperations.swift file and write the following code.

import ErrorTypes

public struct MathOperations
{
     public static func add(Number num1 : Int, with num2 : Int) -> Int
     {
          return num1 + num2
     }

     public static func mult(Number num1 : Int, with num2 : Int) -> Int
     {
          return num1 * num2
     }

     public static func div(Number num1 : Int, by num2 : Int) throws -> Int
     {
          guard num2 > 0
          else
          {
          throw ErrorCodes.DivideByZero("You are dividing by zero. The second argument is incorrect.")
          }

          return num1 / num2
     }

     public static func sub(_ num1 : Int, from num2 : Int) -> Int
     {
          return num2 - num1
     }
}

Before we build we need to modify the Packages.swift file to indicate there is a dependency.
Notice that in the MathOperations.swift file we are importing a module called ErrorTypes. We just created it. But just because we created it doesn’t mean it will be added automatically. We need to pull that module into our own

Also notice that I have provided access specifiers “public” everywhere. This ensures that the code written in one module is accessible in the other.

Navigate to the MathOperations parent folder.
```
cd ~/Developer/SPMDEMO/MathOperations/
```

Open the Packages.swift file and make the changes as shown below:

// swift-tools-version:4.0
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(name: "MathOperations",
     products: [
          // Products define the executables and libraries produced by a package, and make them visible to other packages.
          .library(name: "MathOperations", targets: ["MathOperations"]),
     ],

     dependencies: [
          // Dependencies declare other packages that this package depends on.
          .package(url:"https://github.com/AmaranthineTech/ErrorTypes.git", from:"1.0.0"),
     ],

     targets: [
          // Targets are the basic building blocks of a package. A target can define a module or a test suite.
          // Targets can depend on other targets in this package, and on products in packages which this package depends on.
          .target(name: "MathOperations", dependencies: ["ErrorTypes"]),
          .testTarget(name: "MathOperationsTests", dependencies:   ["MathOperations"]),]
)

Once these changes are made save the file and run the command
```
swift build
```
If you typed everything correctly then you should see the source code for the ErrorTypes module being pulled in and the build being successful.Here are some common mistakes:
– Forgetting to write the import ErrorTypes statement
– Error in the URL
– The from tag not matching the tag in the repository
– Access specifiers are incorrect or missing
– Not mentioning the dependencies in the target
Just like with the ErrorTypes module create a git repository for the MathOperations module.
Now let us make the Calc executable that will use the MathOperations library. First navigate back to the SPMDEMO folder and create a folder called Calc.
```
cd ~/Developer/SPMDEMO/
mkdir Calc
```
This time we are going to create an executable package. Run the command:
```
swift package init --type executable
```
This also creates a similar folder structure as in the case of the library.
Navigate to the folder containing the main.swift file.
```
cd ./Sources/Calc/
```

Modify the main.swift file as shown below:

import MathOperations

//testing addition
var result : Int = MathOperations.add(Number: 33, with: 29)
print("Result of adding 33 with 29 is: \(result)")

//testing multiplication
result = MathOperations.mult(Number: 33, with: 29)
print("Result of multiplying 33 with 29 is: \(result)")

//testing division
do
{
     result = try MathOperations.div(Number: 33, by: 0)
     print("Result of dividing 33 by 29 is: \(result)")
}
catch let error
{
     print("ERROR: \(error)")
}

//testing subtraction
result = MathOperations.sub(3, from: 29)print("Result of subtracting 3 from 29 is: \(result)")

Navigate back to the main Calc folder.
```
cd ~/Developer/SPMDEMO/Calc/
```

Modify the Packages.swift file as shown below:

// swift-tools-version:4.0
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(name: "Calc",
dependencies: [
     // Dependencies declare other packages that this package depends on.
     .package(url: "https://github.com/AmaranthineTech/MathOperations.git", from: "1.0.1"),
],
targets: [
     // Targets are the basic building blocks of a package. A target can define a module or a test suite.
     // Targets can depend on other targets in this package, and on products in packages which this package depends on.
     .target(name: "Calc", dependencies: ["MathOperations"]),
]
)

Save the file and run the build command:
```
swift build
```
Like before you should see both the MathOperations & ErrorType module being pulled in. We are ready to run the executable. Navigate to the debug folder which contains the executable. Make sure you are in the main Calc folder when you run this command.
```
cd ./build/debug/
```
You should see an executable file called Calc. Run it.
```
./Calc
```
If everything went okay then you should see the output on the console.

As you can see it is pretty straightforward to develop Applications written in Swift on Linux.

Adding System Modules

In the previous example we saw how to import our own custom made modules. However, there are some modules provided by the system which offers functionality we may wish to use. For example if we wanted to use the random number generator in our application we would need to use the random() method. This is in the glib module.

Quickly create a package called SystemLibs. This is an executable.

Write the following code in the main.swift.

#if os(Linux)
import Glibc
#else
import Darwin.C
#endif
extension Int
{
     func toString() -> String
     {
          return "\(self)"
     }
}

var luckyNumber : Int = Int(random())

var luckyNumberStr : String = luckyNumber.toString()

print("The lucky number is \(luckyNumberStr)")

Build the code and run the executable.

Adding system modules is direct and simple. The glibc module contains aspects of the standard library. The condition check is to make sure that we are importing the correct module based on the system that we are developing the application on.

Handling Sub-dependencies

As we saw in the earlier example, sub dependencies are handled automatically. So when our Calc application marked the MathOperations module as a dependency it was pulled during the build. However, the MathOperations module itself marked ErrorTypes module as a dependency. We did not have to modify the Packages.swift file belonging to Calc to indicate that ErrorTypes module also needs to be pulled. This was handled automatically by Swift Package Manager.

Conclusion

In this article we have seen:

How to create a library package
How to create a library package that depends on another library package
How to create an executable that depends on a library package
How to import the system Glibc module into our executables.

The Swift Package Manager simplifies many aspects of the development process for us. Many of the things we have discussed also work on macOS. Going forward reusing code and planning for the same should be done keeping Swift Package Manager in mind.

UPDATE: Swift on Linux

March 27, 2018April 9, 2018 / Arun Patwardhan / 1 Comment

This article is an UPDATE for Writing Swift Programs on Linux

This article uses Command Line Interface(CLI) to write Swift Programs. If you are new to CLI then you should read the following articles: Terminal Commands for OS X – Basic, Terminal Commands for OS X – Part 2.

This article has been written using Ubuntu version 16.04 LTS

For the best part the process is still the same.

Download the Swift tools for Linux from: Swift Download Page
Untar the downloaded files
Copy them to a folder of your choice. I have created a folder called “Developer” in my home folder. So I copied the untarred contents there. This is important because we will be needing the location later.
Switch to Terminal on your Ubuntu System.
First we will install clang. Run the command
```
sudo apt-get install clang
```
Next we will make sure we set the PATH to the path where we copied the Swift tools. For example if the Untarred swift folder is called “swift-4.0-DEVELOPMENT-SNAPSHOT-2017-12-04-a-ubuntu16.04/usr/bin:”${PATH}” and it is in the Developer folder I created earlier then the command would be:
```
export PATH=/home/admin/Developer/swift-4.0-DEVELOPMENT-SNAPSHOT-2017-12-04-a-ubuntu16.04/
```
The folder name will vary from system to system. The path above is just an example.
Let us check to make sure that everything installed okay. We can do this with 2 commands:
```
which swift
```
This should show you the path to the folder.
or
```
swift --version
```
This should print out the swift version.

Next let us test the REPL. Run the command:

swift

This will result in a prompt that looks like:

Welcome to Swift version 4.0.3-dev (2dedb62a0b, Clang ab7472e733, Swift 64ab6903b2). Type :help for assistance.
 1>

Type some of the commands mentioned below:

12 * 8
let hello = "Welcome to Swift in Linux"
print(hello)

Now that we know that the REPL is working well, let us move on to the next stage. Let us quit from the REPL:
```
:q
```

Creating Single File Projects

Next let us use Swift Package Manager to create a single file project. I will be creating the project in the Developer folder. So I will navigate to it:cd ~/Developer/
Create a folder of your choice, lets call it Hello World:
```
HelloWorld
```
Enter the folder:
```
cd HelloWorld
```
Create a manifest file for the Package with the command:
```
swift package init
```
This will create some content for you. The structure should look as shown below.
If we run the command to build it will simply create a module for us. To do that type and run:
```
swift build
```
But we would like to create an executable application. In the sources folder create a file called main.swift. You can use the command:
```
touch main.swift
```
to quickly create a new swift file.

Open the main.swift file. Write the following code in there:

let object : HelloWorld = HelloWorld()
print(object.text)
print("End of program...!")

To create the executable we will first build our code:
```
swift build
```
Now we will run the executable, assuming that you are still in the HelloWorld folder within the sources folder navigate to a hidden build folder. To do that first we will navigate to our main HelloWorld package folder.
```
cd ../..
```
To view all the folders including the hidden folders run the list command:
```
ls -la
```
Navigate to the hidden folder and the debug folder inside it to locate the executable:
```
cd .build/debug/
```
To run the executable:
```
./HelloWorld
```
If you want to build and directly run & avoid doing steps 9-13 repeatedly the command is:
```
swift run
```

Next we will see how to create multi file projects

Create Multi File Projects

In the previous project go back to the HelloWorld folder within the Sources folder. Create a file called converter.swift:
```
touch converter.swift
```

Write the following code in that file:

//note the code below is for demonstrating multi file projects & may not necessarily be accurate or correct

//note the code below is for demonstrating multi file projects & may not necessarily be accurate or correct
func centigrade_to_fahrenheit(temperatureInCentigrade : Float) -> Float
{
     return ((temperatureInCentigrade*9.0/5.0)+32.0)
}

func string_to_float(input : String) -> Float
{
     var number : Float = 0.0;
     var result : Float = 0.0
     var decimalFound : Bool = false
     var numberOfDigitsAfterDecimal : UInt8 = 0

     for charac in input
     {
          switch charac
          {
               case "0":
                    number = 0.0;
                    result = (result * 10.0) + number;
               case "1":
                    number = 1.0;
                    result = (result * 10.0) + number;
               case "2":
                    number = 2.0;
                    result = (result * 10.0) + number;
               case "3":
                    number = 3.0;
                    result = (result * 10.0) + number;
               case "4":
                    number = 4.0;
                    result = (result * 10.0) + number;
               case "5":
                    number = 5.0;
                    result = (result * 10.0) + number;
               case "6":
                    number = 6.0;
                    result = (result * 10.0) + number;
               case "7":
                    number = 7.0;
                    result = (result * 10.0) + number;
               case "8":
                    number = 8.0;
                    result = (result * 10.0) + number;
               case "9":
                    number = 9.0;
                    result = (result * 10.0) + number;
               default:
                    decimalFound = true
                    break
          }
          if decimalFound
          {
               numberOfDigitsAfterDecimal += 1
          }
     }

     for _ in 0..<numberOfDigitsAfterDecimal-1
     {
          result = result / 10.0
     }
     return result
}

Write the following code in the main.swift file:

let object : HelloWorld = HelloWorld()
if CommandLine.arguments.count != 2
{
        print("USAGE: centigradeToFahrenheit 33.4")
        print("You are missing an argument")
}
else
{
        let temperatureInCentigrade = string_to_float(input: CommandLine.arguments[1]) 

        print("\(temperatureInCentigrade) is equal to \(centigrade_to_fahrenheit(temperatureInCentigrade: temperatureInCentigrade))")
}
print(object.text)
print("End....!")

Build and run the code. To run it while passing arguments in:
```
./HelloWorld 33.4
```

So that is how you can build single file & multi file Swift applications on Linux.

Programming Style Guide: Documentation

December 24, 2017 / Arun Patwardhan / 1 Comment

Now we will shift our attention to that part of programming which is often ignored. Documentation.

Documentation is a key part of programming. In fact, some might go as far as saying that Documentation is the most important aspect of Programming. Let us understand what we mean by documentation by looking at some key points. Later we will look at different ways of documenting our code.

We document our code so that:

Anyone who is reading our code can understand what we are trying to achieve.
Anyone who wishes to make changes to our code knows where to make the changes.
Anyone who issuing our code can easily find out its capabilities and limitations.
Other programmers can figure out how to use our code.
Developers can find out when and where changes were made to a code. This is useful to understand the evolution of our code.
We can easily recollect what, why, when, where & how something was done by us. This is necessary if we are revisiting code that we have written a long time back.
We can add warnings and disclaimers

There may be some other reasons why we may want to document our code, but the list above summaries the most common reasons. This can easily be seen from a simple example.

func fahr_to_cent(Centigrade temp : Float) -&amp;gt; Float
{
return (32 + (temp * 1.8))
}

It is clear to use what the function does simply from its name. However, there is a lot more information that we can provide. Let us modify the implementation a little bit to make it more informative and readable.

/**
This function takes temperature in Centigrade and converts it to Fahrenheit.
- important: This function does not do data validation
- parameter temp: This is the temperature in Centigrade. It can be a negative value too.
- returns: This is the temperature in Fahrenheit.
- requires: `temp > -273.0 && temp < 1000.0`
- Note: The requirement mentioned is not enforced.
- Since: iOS 11
- author: Arun Patwardhan
- copyright: Copyright (c) Amaranthine 2015
- version: 1.0
*/
func convert_to_fahrenheit_from(Centigrade temp : Float) -&amp;gt; Float
{
     return ((temp * 9.0 / 5.0) + 32.0)
}

The code above looks a lot better now. We made the function name better, but more importantly we have added documentation that better describes the function. This includes range of permitted values, version number, important notes. The comments haven’t been written randomly. They have been formatted in a way that will make them appear in quick help. So now if we have to use the function we know what to watch out for.

Now that we know why we need to document our code let us look at some of the ways this can be done.

Comments

The most common form of documentation is by using comments. Most programming languages support comments. Comments are text which is ignored by the compiler. As such they are not used to build the actual software. The sole reason why they exist is because there has to be some mechanism to write notes.

Single Line Comments

// This is a comment

A single line comment as the name says is a piece of text that can fit in one line.

Good when a short description is required. Normally this is placed before or after a variable as most variables would need a short description.

You can have multiple lines using the Single comment mechanism too.

// This is a comment
// This is a comment on the next line

Multi Line Comments

There is a better way to implement multi line comments. We can enclose the text in a /* */ range.

/* This is a comment
   This is a comment on the next line
   Useful when we have to write really large pieces of comments&amp;amp;amp;lt;span 				data-mce-type="bookmark" 				id="mce_SELREST_start" 				data-mce-style="overflow:hidden;line-height:0" 				style="overflow:hidden;line-height:0" 			&amp;amp;amp;gt;&amp;amp;amp;lt;/span&amp;amp;amp;gt;
*/

Use Case

Here are some examples of when comments can or should be used.

/*
        File Name.   : main.cpp
        Date Created : 13th February 2017
        Created By   : Arun Patwardhan
        Project Name : String Parser
        File Contents:
                - Command Line Option selector
                - Different entry points for the remaining code
        Contact      : arun@amaranthine.co.in
*/

This is a classic example of a multi line comment. This comment provides useful information about the name of the file, when it was created, who created it, contact information, the code that is found in this file.

/*
    Exception Possibilities while Reading/Writing from/to Database
    write_error : This is thrown when there is duplicate data that is being
                  written into the database.
    db_empty.   : This is thrown when you attempt to read from an empty data
                  base.
                  Use the func is_empty() method.
    invalid_data: This is thrown when the data to be written is not valid.
    data_missing: This is thrown when insufficient data is passed. If the write
                  operation requires mandatory data an exception is thrown
                  instead of writing default values.
*/
enum DBExceptions : Error
{
    case write_error(String)
    case db_empty(String)
    case invalid_data(String)
    case data_missing(String)
}

This example shows the necessary documentation while declaring a new type. In short its purpose and situations when different values might be used.

Here is an example of code for functions.

@interface Converter : NSObject
/*!
    @brief This is a temperature conversion function

    @discussion This functions takes floating point values and does a floating point conversion to make sure that we get a precise conversion.

    @param temperature This is the value in centigrade that is passed in. Note, negative values can also be passed in. Values whose results exceed the range supported by float will produce un predictable results.

    @return float Returns a floating point value
*/
-(float) convert_to_fahrenheit_from_centigrade:(float) temperature;
@end

The comment gives information about different aspects of the function. Including the rage of values supported. Note that it also uses special markup to allow for the code description to show up in the Help menu bar or when you option click the method.

This is how the comments with markup look like. They appear in the ⌥ click menu as well as the help menu on the right hand side.

Read Me Files

Another thing one can do along with comments is to create Read Me files. Read Me files are plain text files that are bundled as a part of the project. Unlike comments which give information about a specific piece of code or an entire file, Read Me files give information about the entire project as a whole. Since they are text files we actually treat them as text.

Here is some typical information that is found in a Read Me file:

Project Name : String Parser
Project Request/Ticket Code: 13788
Orignal Project Author : Arun Patwardhan
Contact Details :
– arun@amaranthine.co.in
– http://www.amaranthine.in

Platforms on which Application Can Run
– macOS 10.10 or later
– Windows 7 or later
– Linux (Ubuntu 14 or later)

Compiler Supported – g++

Building the Application

make

Testing

strParser -f Test1 -o myOutput1
strParser -f Test2 -o myOutput2

Files
– makefile
This is the file used to build the Application.

– main.cpp
This is the entry point file. The selection of execution path on the basis of command line options is done here.

– Parser.h
This file contains the declaration for the Parser class as well as its internal structure.

– Parser.cpp
This file contains the implementation of the Parser class

– DataStructure.h
This file contains the declaration of the internal structure of the data structure.

– DataStructure.cpp
This file contains the implementation of the internal structure of the data structure.

– Validator.h
This file contains the declaration of the internal structure of the data structure.

– Validator.cpp
This file contains the implementation of the internal structure of the data structure.

– Test1
Runs a basic set of strings as input.

– Output1
Expected output after running Test1. Compare your results with the results of this file.

Libraries Required – Standard Template Library

The above is just a sample Read Me file. In real world implementations these can get a lot bigger with references to links and future developments. Some of the other things that can be mentioned are:

Future additions
Bugs fixed (potentially with the bug fix request ticket)
Limitations
Tools that are required to make this code
Additional tools that need to be installed
Project Status

Naming Conventions

Documentation becomes a lot easier if we follow good naming conventions. Variables, functions, types, files… which are well named in itself become self explanatory and at the very least reduce the amount of documentation required.

Additional Tools Documentation in C++, Objective-C

Doxygen

HeaderDoc – retired You may come across some projects that use this.

Additional References for Documentation for Swift

Here is an article on Markups for Swift.

What are custom operators?

Why do we need them?

What do we need to create custom operators?

Operator Rules

Operator types

Allowed Characters

Whitespace

Operator grammar

Examples

Operator Precedence

Creating the operators

Summary the new operator

Download the sample project

Video

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What are code snippets?

How do we create code snippets?

Placeholder

Dragging snippets

Exporting code snippets

Summary

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Getting Started

Download

Disclaimer

WARNING

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What are “nibless” apps?

Why should we create Apps without storyboard?

How can we create Apps without Storyboard?

Are there any benefits of creating apps without storyboard?

Are there any drawbacks?

Note

Download the Source Code

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Points to Note:

Getting Started

Creating the Reusable Framework

Using the Framework in a project

Link to Sample Code

Video

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Command Query Separation

Command Functions

Query Functions

Returning Error Codes

Passing An Error Code variable

Exceptions & Exception Handling

Conclusion

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1. Do we want to migrate?

2. Preparing to Migrate

3. Starting the Migration

Migration Steps

5. Things to watch out for

6. Full Conversion versus Part by Part Conversion

Full Conversion

Part Conversion

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About Swift Package Manager

Modules

Targets

Packages

Products

Dependencies

End Products

Example

Creating a Package

Adding System Modules

Handling Sub-dependencies

Conclusion

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