Closed
Description
| Previous ID | SR-11818 |
| Radar | rdar://problem/57369535 |
| Original Reporter | Alvae (JIRA User) |
| Type | Bug |
| Status | Resolved |
| Resolution | Done |
Environment
macOS 10.14.6
Apple Swift version 5.1.2 (swiftlang-1100.0.278 clang-1100.0.33.9)
Target: x86_64-apple-darwin18.7.0
Additional Detail from JIRA
| Votes | 0 |
| Component/s | |
| Labels | Bug |
| Assignee | None |
| Priority | Medium |
md5: fbb65ac0c98f2c39a39b37ff1ba9c5f0
Issue Description:
The following code has undefined behavior:
protocol Boxable {
func boxed() -> Self
}
class List: Boxable {
let next: List?
init(next: List?) { self.next = next }
func boxed() -> Self { List(next: self) as! Self }
}
class DerivedList: List {
let foo: String
init(foo: String, next: List?) { self.foo = foo; super.init(next: next) }
}
let derived = DerivedList(foo: "bar", next: nil).boxed()
print(derived.foo)I would have expected the downcast to Self in List.boxed() to crash the program when I called boxed on DerivedList's instance. As it didn't, the property derived.foo is actually uninitialized.