在Swift中从嵌套数组读取的正确语法？

Question

Essentially I'm trying to grab in integer from an Array -> Dictionary -> Array -> Int. What I have produces no console errors and compiles fine, but always returns 0. I think my syntax is wrong but I'm not sure of the correct way to rewrite it.

convenience init(fromDict dict: [String: Any]) {
    let dfa = dict["forms"] as? Array<Dictionary<String,Array<Any>>>
    self.init(
        heart: dfa?[0]["abilities"]?[0] as? Int ?? 0
    )
}

<array> <dict> <key>forms</key> <array> <dict> <key>abilities</key> </array> <integer>65</integer> </array>

Answer 1

Your syntax looks ok to me, although I would suggest making the inner array contain Int rather than Any if it will always contain ints. That way you can lose that final cast to Int type.

If either of your conditional casts fails then you'll get nil, and the nil coalescing operator will convert your nil into a 0. I suggest writing debug code that logs the object passed into your init method, and then casting one thing at a time and stepping through to see where it fails.

(As Matt says in his comment, if the first conditional cast fails, your dfa variable will be nil.)