Marshaling Date?

[JetForMe]

So, it's clear to me how to unmarshal a Date, by extending it with the ValueType protocol. But it's not at all clear how to marshal it. I tried various forms of this:

extension
Date : ValueType, Marshaling
{
	public
	static
	func
	value(from inObj: Any)
		throws
		-> Date
	{
		guard
			let timeInterval = inObj as? Double
		else
		{
			throw MarshalError.typeMismatch(expected: Double.self, actual: type(of: inObj))
		}
		
		let date = Date(timeIntervalSinceReferenceDate: timeInterval)
		return date
	}
	
	public
	func
	marshaled()
		-> Double
	{
		return self.timeIntervalSinceReferenceDate
	}
}

But Xcode doesn't like it. In this case, it says Type 'Date' does not conform to protocol 'Marshaling'. Not sure what I'm doing wrong.