Mapping dictionaries in Swift

Dictionary.swift

extension Dictionary {
    public func map<T: Hashable, U>(@noescape transform: (Key, Value) -> (T, U)) -> [T: U] {
        var result: [T: U] = [:]
        for (key, value) in self {
            let (transformedKey, transformedValue) = transform(key, value)
            result[transformedKey] = transformedValue
        }
        return result
    }
    
    public func map<T: Hashable, U>(@noescape transform: (Key, Value) throws -> (T, U)) rethrows -> [T: U] {
        var result: [T: U] = [:]
        for (key, value) in self {
            let (transformedKey, transformedValue) = try transform(key, value)
            result[transformedKey] = transformedValue
        }
        return result
    }
}

let dict = ["A": "a", "B": "b"]
dict.map { (key, value) in
    (key.lowercaseString, value.uppercaseString)
}
// Result is ["a": "A", "b": "B"]