Reflection and typeChecking for optionals - reflection

Question

Playing with reflections in swift 2.0 i'm trying to type check a child value.
The problem: each element of the children array in the Mirror of Any item is not optional, but his type can be optional... What happens is that of course i have the child value even if the value is nil
Maybe it is not clear so i put here some code to explain better.
For convenience i defined a subscript in a Mirror extension that fetches the child object with a given label
extension Mirror {
public subscript(key: String)->Child?{
var child = children.filter {
var valid = false
if let label = $0.label {
valid = label == key
}
return valid
}.last
if child == nil,
let superMirror = superclassMirror() {
child = superMirror[key]
}
return child
}
}
perfect, now let's say i have this class
class Rule: NSObject, AProtocol {
var hello: String?
var subRule: Rule?
}
Ok, now the problem
let aRule = Rule()
let mirroredRule = Mirror(reflecting:aRule)
if let child = mirroredRule["subRule"] {
//child.value always exists
//i can't do child.value is AProtocol? because child.value is not optional
//child.value is AProtocol of course returns false
//child.dynamicType is Optional(Rule)
if let unwrapped = unwrap(child.value) where unwrapped is AProtocol {
//This of course works only if child.value is not nil
//so the unwrap function returns an unwrapped value
//this is not a definitive solution
}
}
child.value has not been initialized so it is nil, and i can't check his type using the unwrap function. I'm writing a deserializer so i need to check the var also if it is nil because in the dictionary that will be used for the deserialization it could be defined.
private func unwrap(subject: Any) -> Any? {
var value: Any?
let mirrored = Mirror(reflecting:subject)
if mirrored.displayStyle != .Optional {
value = subject
} else if let firstChild = mirrored.children.first {
value = firstChild.value
}
return value
}
I hope the problem is clear. Any suggestions?

Answer 1

Based on this answer, I recommend using if case Optional<Any>.some(_).
I did something recently to make sure I have at least one optional set on my struct. You can paste into playgrounds:
struct ErrorResponse: Codable {
let message: String?
let authorizationException: [String: String]?
let validationException: String?
let generalException: String?
var isValid: Bool {
var hasAtLeastOneNonNilErrorValue = false
Mirror(reflecting: self).children.forEach {
if case Optional<Any>.some(_) = $0.value {
hasAtLeastOneNonNilErrorValue = true
}
}
return hasAtLeastOneNonNilErrorValue
}
}
let errorTest = ErrorResponse(message: "some message", authorizationException: nil, validationException: nil, generalException: nil)
let errorTest2 = ErrorResponse(message: nil, authorizationException: nil, validationException: nil, generalException: nil)
print("is valid: \(errorTest.isValid)") //is valid: true
print("is valid: \(errorTest2.isValid)") //is valid: false