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MahatmaManic
MahatmaManic

Reputation: 953

In Swift, how can I directly modify an array stored in a dictionary?

I am writing an iPhone app in Swift. I have a dictionary that maps String keys to [MyClass] values. I have a function that does the following:

func addItem(object: MyClass) -> Bool {
    if self.dict[object.name] == nil {
        self.dict[object.name] = [MyClass]()
    }

    var objectList = self.dict[object.name]!

    // Other code here that doesn't matter 

    objectList.append(object)
    return true
}

The problem here is that when I reach the return statement, "objectList" has a count of 1, but self.dict[object.name]! has a count of 0. That is to say that objectList is actually a copy of the array in the dictionary rather than the same array.

I guess that makes some sense, since arrays are value types in Swift, but it's pretty inconvenient. Does anyone have a good solution for this? Can I force the return from the dictionary to a reference a la inout? Or do I need to create my own list class to wrap arrays with or save modified arrays back to the dictionary?

Upvotes: 2

Views: 227

Answers (1)

Nate Cook
Nate Cook

Reputation: 93276

You need to append it to the array inside the dictionary:

self.dict[object.name]!.append(object)

What's happening is that a Dictionary instance's subscript returns an Optional, since there's no guarantee that the dictionary actually has a value for the key you pass in. You can assign through either of the unwrapping operators (? or !) - in this case the force unwrapping is okay since you test and create the array above.

Upvotes: 2

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