Attempting to make NSDateComponents conform to DictionaryLiteralConvertible

NSDateComponents+DictionaryLiteral.swift

import Cocoa

public extension NSDateComponents {
    public convenience init(_ components: DictionaryLiteral<NSCalendarUnit, Int>) {
        self.init()
        for (key, value) in components {
            setValue(value, forComponent: key)
        }
    }
}

print(NSDateComponents([.Hour: 10, .Minute: 30]))

//extension NSDateComponents: DictionaryLiteralConvertible {
//    public typealias Key = NSCalendarUnit
//    public typealias Value = Int
//
//    public convenience init(dictionaryLiteral elements: (NSDateComponents.Key, NSDateComponents.Value)...) {
//        self.init()
//    }
//}
//

// That extension fails:
// Initializer requirement 'init(dictionaryLiteral:)' can only be satisfied by a `required` initializer in the definition of non-final class 'NSDateComponents'