What is the difference between `let` and `var` in swift?

Question

What is the difference between let and var in Apple\'s Swift language?

In my understanding, it is a compiled language but it does not check

Answer 1

let keyword defines a constant

let myNum = 7

so myNum can't be changed afterwards;

But var defines an ordinary variable.

The value of a constant doesn’t need to be known at compile time, but you must assign it a value exactly once.

You can use almost any character you like for constant and variable names, including Unicode characters;

e.g.

var x = 7 // here x is instantiated with 7 
x = 99 // now x is 99 it means it has been changed.

But if we take let then...

let x = 7 // here also x is instantiated with 7 
x = 99 // this will a compile time error

Answer 2

Declare constants with the let keyword and variables with the var keyword.

let maximumNumberOfLoginAttempts = 10 var currentLoginAttempt = 0   
let maximumNumberOfLoginAttempts = 10
var currentLoginAttempt = 0

Declare multiple constants or multiple variables on a single line, separated by commas:

var x = 0.0, y = 0.0, z = 0.0

Printing Constants and Variables

You can print the current value of a constant or variable with the println function:

println(friendlyWelcome)

Swift uses string interpolation to include the name of a constant or variable as a placeholder in a longer string

Wrap the name in parentheses and escape it with a backslash before the opening parenthesis:

println("The current value of friendlyWelcome is \(friendlyWelcome)")

Reference : http://iosswift.com.au/?p=17

Answer 3

var is the only way to create a variables in swift. var doesn't mean dynamic variable as in the case of interpreted languages like javascript. For example,

var name = "Bob"

In this case, the type of variable name is inferred that name is of type String, we can also create variables by explicitly defining type, for example

var age:Int = 20

Now if you assign a string to age, then the compiler gives the error.

let is used to declare constants. For example

let city = "Kathmandu"

Or we can also do,

let city:String = "Kathmandu"

If you try to change the value of city, it gives error at compile time.

Answer 4

SIMPLE DIFFERENCE

let = (can not be changed)

var = (any time update)

Answer 5

let is used to define constants and var to define variables. You define the string using var then particular String can be modified (or mutated) by assigning it to a variable (in which case it can be modified), and if you define the string using let its a constant (in which case it cannot be modified):

var variableString = "Apple"
variableString += " and Banana"
// variableString is now "Apple and Banana"

let constantString = "Apple"
constantString += " and another Banana"
// this reports a compile-time error - a constant string cannot be modified

Answer 6

“Use let to make a constant and var to make a variable”

Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. https://itun.es/us/jEUH0.l