var to let type conversion or vice versa in swift:

Question

Can a var type be changed into let type or vice versa in swift. I try to search it online but there is no such content available online.

Answer 1

You cannot change the mutability of a variable once it has been declared. However, you can create a mutable/immutable copy of any variable.

let immutable = 21
var mutableCopy = immutable
mutableCopy = 2

var mutable = 3
let immutableCopy = 4

You also have to be aware though that mutability and copying means different things for reference and value types.

Answer 2

conversion from let to var

let a = "" /* Constant */
var b = a /* Variable */
b = "b"

conversion from var to let

var c = "" /* Variable */
let d = c /* Constant */

Declaring Constants and Variables Constants and variables must be declared before they’re used. You declare constants with the let keyword and variables with the var keyword. source

Struct (Value Type) vs Class (Reference Type)

class TotoClass {
    var str = "str"
}

struct TotoStruct {
    var str = "str"
}

let classToto = TotoClass()
let structToto = TotoStruct()

classToto.str = "new Str"
structToto.str = "new Str"

last line doesn't compile and there will be an error

Cannot assign to property: 'structToto' is a 'let' constant