Object in array not being modified

Question

I have this function that is supposed to find a "Buyer" object and modify the "amount" and "items" attribute of that buyer object.

Here is the code:

    func itemsToBuyers() {
        buyers = []
        for item in items! {
            for buyer in item.buyers {
                var result = buyers.filter({$0.name == buyer}).first
                if result == nil {
                    //add the buyer to the buyers array
                    let name: String = buyer
                    let amount: Float = Float(String(format: "%.2f", item.price/Float(item.buyers.count)))!
                    let items: [String] = [item.name]
                    let newBuyer = Buyer(expanded: false, name: name, amount: amount, items: items)
                    buyers.append(newBuyer)
                } else {
                    //update the amount and item list of buyer
                    print("adding")
                    result?.amount += Float(String(format: "%.2f", item.price/Float(item.buyers.count)))!
                    result?.items.append(item.name)
                }
            }
        }
    }

The initial insertion of each new Buyer object works fine, but the else statement is not behaving as expected. The code is being run and "adding is printed", but the object is not actually being modified.

Specifically, is it a struct or a class? Structs are value types — Paulw11
– Paulw11, Commented Mar 24, 2020 at 21:13
I changed it from struct to class. This solved my problem. Thanks! — Jack Wu
– Jack Wu, Commented Mar 24, 2020 at 22:01

HalR · Accepted Answer · 2020-03-24 21:20:17Z

1

When you make this call

var result = buyers.filter({$0.name == buyer}).first

you are copying into result. When you change result later, it has no impact on the buyers array. These two lines change result, but not buyers:

result?.amount += Float(String(format: "%.2f", item.price/Float(item.buyers.count)))!
result?.items.append(item.name)

If buyer were not a value type, then you could be dealing with pointers instead of copied values and this approach could work.

answered Mar 24, 2020 at 21:20

HalR

11.1k5 gold badges51 silver badges86 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jack Wu Over a year ago

I initially had the buyer object declared as a struct. I changed it to class, and that solved my problem. Thank you!

Collectives™ on Stack Overflow

Object in array not being modified

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related