koher

struct Foo { var a: Int = 42 } struct Bar { var foo: Foo = Foo() } extension KeyPath { func appending(path: PartialKeyPath<Value>) -> PartialKeyPath<Root> { return (self as AnyKeyPath).appending(path: path as AnyKeyPath)! as! PartialKeyPath<Root> } } let k1: WritableKeyPath<Bar, Foo> = \.foo let k2: PartialKeyPath<Foo> = \.a let k: PartialKeyPath<Bar> = k1.appending(path: k2) let bar = Bar() let a: Any = bar[keyPath: k] print(a)

Version:

swift-4.1.1-RELEASE

Output:

42

Error: