Counterpart methods to `mapValues(_:)` and `compactMapValues(_:)`

Dictionary+MapKeys.swift

//
//  Dictionary+MapKeys.swift
//
//  Created by Felix Mau on 14.06.21.
//  Copyright © 2021 Felix Mau. All rights reserved.
//

extension Dictionary {
    /// Returns a new dictionary containing the keys transformed by the given closure.
    /// The values of this dictionary stay the same.
    func mapKeys<T: Hashable>(_ transform: (Key) -> T) -> [T: Value] {
        reduce(into: [T: Value]()) {
            let mappedKey = transform($1.key)
            $0[mappedKey] = $1.value
        }
    }

    /// Returns a new dictionary containing the keys transformed by the given closure and filtered by `nil` results.
    /// The values of this dictionary stay the same.
    func compactMapKeys<T: Hashable>(_ transform: (Key) -> T?) -> [T: Value] {
        reduce(into: [T: Value]()) {
            guard let mappedKey = transform($1.key) else { return }

            $0[mappedKey] = $1.value
        }
    }
}