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iOS

Posted by Fabricio Puerto
Fabricio Puerto
2,549 Points

My InventoryUnarchiver crashes the app, but it's the same as the teacher's note!

Here is the teacher's version:

class InventoryUnarchiver {
    class func vendingInventoryFromDictionary(_ dictionary: [String : AnyObject]) throws -> [VendingSelection : ItemType] {

        var inventory: [VendingSelection : ItemType] = [:]

        for (key, value) in dictionary {
            if let itemDict = value as? [String : Double],
                let price = itemDict["price"], let quantity = itemDict["quantity"] {

                let item = VendingItem(price: price, quantity: quantity)

                guard let key = VendingSelection(rawValue: key) else {
                    throw InventoryError.InvalidKey
                }

                inventory.updateValue(item, forKey: key)

            }
        }

        return inventory

    }
}

Here is my version:

class InventoryUnarchiver {
    class func vendingInventoryFromDictionary ( dictionary: [String: AnyObject]) throws -> [ VendingSelection: ItemType] {

        var inventory: [VendingSelection: ItemType]  = [:]
        for (key, value) in dictionary {
            if let itemDict = value as? [String: Double],
            let price = itemDict["price"], let quantity = itemDict["quantity"] {

                let item = VendingItem(price: price, quantity: quantity)

                guard let key = VendingSelection(rawValue: key) else {
                    throw InventoryError.InvalidKey
                }

                inventory.updateValue(item, forKey: key)

            }
        }

        return inventory

    }
}

It looks the same, but for some reason my version crashes the app, and when I just copy the teachers version instead of mine it works. Any idea why???!!

Michael Hulet
Michael Hulet
47,913 Points

Can you post a copy of the crash log and maybe a stack trace of the crash? What line is it crashing on?

1 Answer

Jennifer Nordell
seal-mask
STAFF
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher
Jennifer Nordell
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Hi there! I can see at least something that's not 100% the same as the teacher's version. In the teacher's version (at the very beginning) you'll see this:

(_ dictionary: [String : AnyObject])

But yours looks like:

( dictionary: [String: AnyObject])

Note the underscore in the teacher's version preceding the word "dictionary".

Let me know if this helps! :sparkles:

Michael Hulet
Michael Hulet
47,913 Points

For what it's worth, this is just a matter of calling semantics. In a newer version of Swift (definitely Swift 3, probably Swift 2, maybe even Swift 1), this would cause a compilation error, not a crash. Judging by the source code, this app is written in at least Swift 2.2