How to reassign a variable's value inside a struct? - swift

Question

I have a struct "Person" which I want to reassign each individual object's amount from the structArray which I declared. When I do a for each loop to reassign the amount, an error says
Left side of mutating operator isn't mutable: 'person' is a 'let' constant
struct Person {
let name : String
var amount : Double
}
var structArray:[Person] = []
func calculateBill(pax: [Person]) -> [Person] {
for person in pax {
person.amount += taxByPerson //error
}
return pax
}
What is causing the issue and how can I fix this to be able to reassign the value?
EDIT: Thanks guys for pointing out where my error was, although the downvoting is pretty depressing to watch lol.
func calculateBill(pax: [Person]) -> [Person] {
var finalBill:[Person] = pax
for i in 0..<finalBill.count {
finalBill[i].amount += taxByPerson
}
return finalBill
}

Answer 1

Value types could be a pain and passed parameters are constants (let) by definition.
You could pass the array as an inout parameter, in the function add the value directly in the array:
func calculateBill(pax: inout [Person]) {
for index in 0..<pax.count {
pax[index].amount += taxByPerson
}
}
and call it
calculateBill(pax: &structArray)

Answer 2

Well the error is exactly what it says on the tin... person is a let context. You'll need to use var. But this is more easily accomplished with map
struct Person {
var name: String
var amount: Double
}
var people = [Person]()
func calculateBill(_ people: [Person]) -> [Person] {
return people.map{
var p = $0
p.amount += taxByPerson
return p
}
}