Hi,
I hope everybody had a great New Year celebration.
I was tracking down a weird bug in my Swift code today. A property defined in a
class in order to conform to a protocol was not being seen. A protocol
extension provided a default value of `nil` for this property, so I knew where
it was coming from. Turned out, in my class I had defined the property with the
correct name but incorrect type - I declared it as `String` instead of
`String?`.
I isolated this behaviour in a playground, shown below, and it is pretty weird
behaviour.
The output is:
Something1 has id: nil
Something2 has id: nil
Something3 has id: Correct
-- Direct access--
Something1 - nil
Something2 - nil
Something2 with String(describing:) - Wrong but compiles, returns wrong value
Something3 - Correct
The playground code:
======================
protocol Trackable {
static var analyticsID: String? { get }
}
extension Trackable {
static var analyticsID: String? { return nil }
}
class Something1: Trackable {
}
class Something2: Trackable {
static var analyticsID: String = "Wrong but compiles, returns wrong value"
}
class Something3: Trackable {
static var analyticsID: String? = "Correct"
}
func getID<T: Trackable>(_ trackable: T.Type) {
if let id = trackable.analyticsID {
print("\(trackable) has id: \(id)")
} else {
print("\(trackable) has id: nil")
}
}
getID(Something1.self)
getID(Something2.self)
getID(Something3.self)
print("-- Direct access--")
print("Something1 - \(Something1.self.analyticsID ?? "nil")")
print("Something2 A - \(Something2.self.analyticsID ?? "nil")")
print("Something2 with String(describing:) - \(String(describing:
Something2.self.analyticsID))")
print("Something3 - \(Something3.self.analyticsID ?? "nil")”)
======================
Thanks in advance for any information about my misinterpretations or
recommendations of what parts are actually undesirable so that I can raise the
JIRAs.
Cheers
—
Marc Palmer
Montana Floss Co. Ltd.
Soundproof – Music Player for Practice
http://getsoundproof.com
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