Optional KeyPath Weirdness

optional-weirdness.swift

import Cocoa

class Foo {
    var string = "test"
    var optionalString: String?
}

let foo = Foo()

foo[keyPath: \.string] == nil //false
foo[keyPath: \.optionalString] == nil //true

func value<Object, Type>(of keyPath: ReferenceWritableKeyPath<Object, Type>, for object: Object) -> Any? {
    return object[keyPath: keyPath]
}

value(of: \.string, for: foo) == nil // false
value(of: \.optionalString, for: foo) == nil // false