Lowercase Dictionary Keys in Swift - 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

Answer 2

Smth like that?
var dict = ["KEY": "value"]
var newDict = [String: AnyObject]()
for (key, value) in dict {
newDict[key.lowercaseString] = value
}

Answer 3

Arbitur's answer, updated for Swift 3:
extension Dictionary where Key: ExpressibleByStringLiteral {
public mutating func lowercaseKeys() {
for key in self.keys {
self[String(describing: key).lowercased() as! Key] = self.removeValue(forKey: key)
}
}
}

Answer 4

Here is my solution, no force casting, totally safe.
protocol LowercaseConvertible {
var lowercaseString: Self { get }
}
extension String: LowercaseConvertible {}
extension Dictionary where Key: LowercaseConvertible {
func lowercaseKeys() -> Dictionary {
var newDictionary = Dictionary()
for k in keys {
newDictionary[k.lowercaseString] = self[k]
}
return newDictionary
}
}

Answer 5

Just as an alternative to looping, you could use the map function:
func lowercaseKeys () -> Dictionary<String, AnyObject> {
var newDictionary = Dictionary<String,AnyObject>()
Array(keys).map { key in
newDictionary[(key as! String).lowercaseString] = self[key] as? AnyObject
}
return newDictionary
}