Accessing the optional value of a PartialKeyPath in Swift 4 - swift

Question

Using the PartialKeyPath API, how can you access a value of a key path's reference? For example, this works for non-optional values, but not with Optional values.
The issue I'm having is that self[keyPath: keyPath] returns a non-optional Any value.
struct Element {
let name: String
let mass: Double?
func stringValue(_ keyPath: PartialKeyPath<Element>) -> String {
let value = self[keyPath: keyPath]
switch value {
case let string as String:
return string.capitalized
case nil:
return "N/A"
case let value:
return String(describing: value)
}
}
}
let element = Element(name: "Helium", mass: 4.002602)
let string = element.stringValue(\Element.mass) /* Optional(4.002602) */
The result is that case nil is never executed and the last case is being printed as Optional(value).
How can I unwrap value properly to extract the optional?

Answer 1

The solution was to use Mirror to unwrap the optional which seems less than optimal. Looking forward to better Reflection support in Swift!
func unwrap(_ value: Any) -> Any? {
let mirror = Mirror(reflecting: value)
if mirror.displayStyle != .optional {
return value
}
if let child = mirror.children.first {
return child.value
} else {
return nil
}
}
struct Element {
let name: String
let mass: Double?
func stringValue(_ keyPath: PartialKeyPath<AtomicElement>) -> String {
guard let value = unwrap(self[keyPath: keyPath]) else {
return "N/A"
}
switch value {
case let string as String:
return string.capitalized
default:
return String(describing: value)
}
}
}
let element = Element(name: "Helium", mass: 4.002602)
let string = element.stringValue(\Element.mass) /* 4.002602 */