Swift iOS -How come I can loop through an array of class objects and make property changes but not structs [duplicate] - swift

Question

This question already has answers here:
Is Swift Pass By Value or Pass By Reference
(10 answers)
Swift can change struct declared with let if using an index but not if using a loop
(3 answers)
Closed 3 years ago.
If I loop through an array of Class objects I can make changes to a property on it
class Country {
var name: String?
var region: String?
init(name: String?, region: String?) {
self.name = name
self.region = region
}
}
let canada = Country(name: "Canada", region: "North America")
let mexico = Country(name: "Mexico", region: "North Ameria")
let france = Country(name: "France", region: "Europe")
let korea = Country(name: "Korea", region: "Asia")
var countryArr = [canada, mexico, france, korea]
// this works fine
let transformed = countryArr.map { $0.name = "Random" }
But if I try this with Struct objects I get
Cannot assign to property: '$0' is immutable
struct Country {
var name: String?
var region: String?
}
var canada = Country(name: "Canada", region: "North America")
var mexico = Country(name: "Mexico", region: "North Ameria")
var france = Country(name: "France", region: "Europe")
var korea = Country(name: "Korea", region: "Asia")
var countryArr = [canada, mexico, france, korea]
// this gets an error
let transformed = countryArr.map { $0.name = "Random" }

Answer 1

The issue is caused by the fact that structs are value types, so mutating any properties of the struct mutates the struct instance itself as well and the closure input arguments in map are immutable. So when you try to mutate a property $0 in the closure of map, you are trying to mutate $0 itself in case map is called on a collection of value types.
On the other hand, classes are reference types, so mutating a property of a class instance doesn't mutate the instance itself.
A solution for your problem is to create a mutable copy of the struct instance in the map, mutate its name property and return that. There are two solutions, if you have a small number of properties on your type, calling its memberwise initialiser is easier, but if you have a lot of properties and only want to mutate a few, copying the struct and then modifying the necessary properties is the better choice.
let transformed = countryArr.map { Country(name: "Random", region: $0.region) }
let transformed2 = countryArr.map { country->Country in
var copy = country
copy.name = "Random"
return copy
}