Swift - Constants & Variables

Lets talk about Constants and Variables in Swift.

Constants:
As name implies a meaning in programming world, a constant value cannot be changed after assignment. In Swift, a constant can be created using keyword 'let'. Lets create our first constant in Swift and assign a value.

let letNumber = 10.0

Changing the value of this above constant will throw an error.

letNumber = letNumber + 10    //  Cannot assign to ‘let’ value ‘letNumber’


Variables:
A variable is a property that are liable to changes. A variable value can be changed after initialisation or during run time. To create a varaible in Swift, use 'var' keyword.

var varNumber = 20.0

You can change the value of a variable and it will work.

varNumber = varNumber + 10    //  see. it works.

In both examples, we didn't mention the data type of 'letNumber' and 'varNumber' properties. This is because Swift automatically infers the data type of the property based on the value assigned to it. Since we assigned double value, it can also be written like this,

var varNumber: Double = 20.0

Syntax time

To create a property in Swift, we can use 'let' or 'var' keywords based on our requirements. The syntax to create a property is,

keyword  variable_name : data_type  = value

keyword - let, var
variable_name - the property name that is referred to store the value
data_type - the property data type
value - value assigned during initialisation



Same concept applies for Strings too.
let letString = “This is like NSString”
var varString = “This is like NSMutableString"

To summarise the difference between Constant and variable, Constant properties are immutable and variable properties are mutable. Considering the above two strings, you can say 'letString' property resembles NSString and 'varString' property resembles NSMutableString objects in Objective C.

A constant or variable name supports valid unicode characters.

Don't's:
  • Avoid using maths symbols, arrows invalid unicode points , line and box-drawing chars while creating a variable or constants. 
  • Don’t start naming a constant or variable with numbers. It can contain in-between but not on start.

One More Thing:
You might remember the fact that semi-colons (;) are not required at the end of each statement in swift.

Comments

Post a Comment

Popular posts from this blog

Swift - Strings

String To declare a string, use let or var keyword. var greeting = "Hello"   // Mutable string let name = “Alice” // Immutable string let keyword creates an immutable string. var creates a mutable string. To modify a string later in code, use var keyword. let will throw error. Swift provides a list of common methods extending String class. These methods will perform various operations with strings. Let’s have a look at few of those commonly used methods. To check the variable is String type let stringObject = "String here" if stringObject is String { print ("Yes") // Yes } To check if two strings are equal let greet1 = "Hello guest" let greet2 = "Hello world" if greet1 == greet2 { print ("same greeting") } else { print ("different greetings") } To capitalise all the words var greeting = "hello guest" print (greeting.capitalizedString)...
Read more

What's new in Swift 4!

Swift 4 Apple has introduced an update to Swift during its WWDC. Lets discuss some of the new features introduced in Swift 4. String In Swift 4, String has been revised to be a collection again. This gives the feature to reverse, sort and count the characters. Multi-Line String As String literals allows you to create a sequence of characters within quotes (“), Swift 4 starting to support multi-line characters. A multi-line string is enclosed within 3 quotes ("””).   A multi-line can also include unescaped double quotes, carriage return and line feeds. To add a line feed, add a empty line to start and end of the multi-line string.  The indentation defines the spacing between the lines. Example, let singleLineString = “I’m a single line string" let multilineString = “"" I’m a  Multi line string. """ Protocol Composition Swift 4 allows developers to combine multiple protocols into a single type using protocol composition. It will be like ...
Read more

Swift - Classes

Classes This is Part 4 of our Swift tutorial series. To create a class in swift, use class keyword. The properties and methods are declared in the same way as constant and variable. class { init () { } } Let's create a class with functions. class mathsClass { func add (a:Int, b:Int) -> Int { return a+b } } let mathsObject = mathsClass() print (mathsObject.add(a:1, b:1)) // 2 Swift classes supports inheritance . We can create a parent class and inherit its properties in the child class. class Student { func studentName () -> String { return "Alice" } } class ReportCard : Student { } let studentCard = ReportCard() print (studentCard.studentName()) // Alice The above example had the student name in function. Let's create a property and store the value. class Student { var name : String init (studentName : String) { name = studentName } } let student = Student(...
Read more