Lowercase Dictionary Keys in Swift

Question

I need to convert a Dictionary with mixed case keys in the same exact Dictionary but with only lowercase keys.

Here is my attempt (It works but I found this implementation extremely rough)

extension Dictionary {
    func lowercaseKeys()->Dictionary<String, AnyObject>{
        var newDictionary = Dictionary<String,AnyObject>()

        for k in keys{
            if let k_string = k as? String{
                newDictionary[k_string.lowercaseString] = self[k] as? AnyObject
            }
        }
        return newDictionary
    }
}

Can you suggest a more elegant way to solve this problem?

Answer 1

Changes its own keys without the need of a temporary dictionary ;)

var dict = ["HEJ":"DÅ", "NeJ":"tack"]

for key in dict.keys {
    dict[key.lowercaseString] = dict.removeValueForKey(key)
}

print(dict)

[hej: DÅ, nej: tack]

EDIT

I made this extension, its a little dirty for now but I will update it again.

extension Dictionary {
    mutating func lowercaseKeys() {
        for key in self.keys {
            let str = (key as! String).lowercaseString
            self[str as! Key] = self.removeValueForKey(key)
        }
    }
}

var dict = ["HeJ":"Då", "nEJ":"taCK!"]
dict.lowercaseKeys()
print(dict)

["hej": "Då", "nej": "taCK!"]

EDIT 2

extension Dictionary where Key: StringLiteralConvertible {
    mutating func lowercaseKeys() {
        for key in self.keys {
            self[String(key).lowercaseString as! Key] = self.removeValueForKey(key)
        }
    }
}

var dict = ["NamE":"David", "LAST_NAME":"Göransson"]

dict.lowercaseKeys() // Will compile

var dict2 = [0:"David", 0:"Göransson"]

dict2.lowercaseKeys() // Won't compile because Key isn't StringLiteralConvertible