Optional promotion breaks exhaustive switching?

taylorswift · 2023-01-01T20:18:41.896Z

i had always assumed that

case wrapped:

promotes to

case wrapped?:

if the switch parameter is optional.

so i was surprised that the following causes a compiler error:

func test1(bool:Bool?)
{
    switch bool
    {
    case nil, true:
        break
    case false:
        break
    }
}

switch.swift:3:5: error: switch must be exhaustive
    switch bool
    ^
switch.swift:3:5: note: add missing case: '.some(_)'
    switch bool

instead it must be written as:

func test2(bool:Bool?)
{
    switch bool
    {
    case nil, true?:
        break
    case false?:
        break
    }
}

why?

anon9791410 · 2023-01-01T20:38:33.121Z

Also asked at the end of this post. Not answered.

Optional implementation. Nil in switch. And init with `Wrapper` type Using Swift

I saw a question recently on StackOverflow that I attempted to answer... swift - How to declare an `enum` of `enum` that allows for "flattened" `switch` statement? - Stack Overflow Initially my answer was no, you can't do this. But... as pointed out by the OP, it seems that Optional DOES do this. (To a certain degree). I was looking through the implementation of Optional here... swift/Optional.swift at main · apple/swift · GitHub And I tried to created my own enum that had the same behaviour.…

Jumhyn · 2023-01-02T04:31:33.928Z

Looks like a bug to me, I don’t see any reason why this switch shouldn’t be considered exhaustive.

LucianoPAlmeida · 2023-01-02T18:10:04.800Z

This has been reported/discussed recently here Optional boolean doesn't satisfy switch exhaustivity with literal case statements · Issue #61817 · apple/swift · GitHub