Key value mapping for swift dictionaries

KeyValueMap.swift

import UIKit

extension Dictionary {
    init<S: Sequence>(_ pairs: S) where S.Iterator.Element == (Key, Value) {
        self = [:]
        for (k,v) in pairs { self[k] = v }
    }

    func keyValueMap<T: Hashable, S>(_ transform: (Key, Value) throws -> (T, S)) rethrows -> [T: S] {
        var newDict = [T: S]()
        for (k,v) in self {
            let (newK, newV) = try transform(k, v)
            newDict[newK] = newV
        }
        return newDict
    }

    func keyValueFlatMap<T: Hashable, S>(_ transform: (Key, Value) throws -> (T?, S?)) rethrows -> [T: S] {
        var newDict = [T: S]()
        for (k,v) in self {
            let (optionalK, optionalV) = try transform(k, v)
            guard let newK = optionalK, let newV = optionalV else { continue }
            newDict[newK] = newV
        }
        return newDict
    }
}

enum Keys: String {
    case one
    case two
    case three
}

let dict = ["one": 1, "two": 2, "three": 3]
let dictToFlatten = ["one": 1, "two": 2, "three": 3, "four": 4]

let converted = Dictionary(dict.map { (k,v) in (Keys(rawValue: k)!, v)})
converted

let converted2 = dict.keyValueMap { k, v in (Keys(rawValue: k)!, v) }
converted2

let converted3 = dictToFlatten.keyValueFlatMap { k, v in (Keys(rawValue: k), v) }
converted3