Enums with boolean raw values

Using Swift
1

i was rather surprised that this does not work:

extension KYC
{
    @frozen public
    enum Verification:Bool, Equatable, Sendable
    {
        case again = false
        case debut = true 
    }
}

error: raw type 'Bool' is not expressible by a string, integer, 
or floating-point literal

you may ask, why do you even need an enum with a raw type of Bool? and the answer is database schema, because i want to encode this to BSON using RawRepresentable.

2

Certainly seems reasonable to me. It’s nothing you can’t write yourself, but while argument labels make it less common to use an enum instead of a boolean they don’t cover all the circumstances where you’d want to do that.

3

Interesting to see that Bool cannot be conformed and have an automatic synthesis but the lexical structure says: raw-value-literal → numeric-literal | static-string-literal | boolean-literal...

4 Likes
4

i ended up shooting myself in the foot writing this, as this relatively simple sketch segfaults for some reason:

@frozen public
enum BooleanEnum:Equatable, Sendable
{
    case a
    case b
}
extension BooleanEnum:RawRepresentable
{
    @inlinable public
    init?(rawValue:Bool) { self = rawValue ? .a : .b }

    @inlinable public
    var rawValue:Bool { self == .a }
}

@main
enum Main
{
    @inline(never) static
    func getBooleanCase() -> BooleanEnum
    {
        return .a
    }

    static
    func main() async throws
    {
        let _state:BooleanEnum = Self.getBooleanCase()
        let hidden:Bool = _state != .a

        print(hidden)
    }
}

$ swiftc crash4.swift -parse-as-library
$ ./crash4

💣 Program crashed: Bad pointer dereference at 0x00007ffd9c0beff8

Thread 0 "crash4" crashed:

     0 0x0000557fe2b3db1b BooleanEnum.rawValue.getter + 27 in crash4
     1 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
     2 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
     3 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
     4 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
     5 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
     6 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
     7 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
     8 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
     9 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    10 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    11 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    12 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    13 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    14 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    15 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    16 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    17 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    18 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    19 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    20 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    21 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    22 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    23 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    24 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    25 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    26 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    27 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    28 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
    29 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
    30 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
   ... 
112230 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
112231 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
112232 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
112233 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
112234 0x0000557fe2b3db3e BooleanEnum.rawValue.getter + 61 in crash4
112235 0x00007f050bf5986d == infix<A>(_:_:) + 124 in libswiftCore.so
112236 0x0000557fe2b3dd50 static Main.main() + 207 in crash4
112237 0x0000557fe2b3dfe0 static Main.$main() in crash4

i haven’t had time to investigate exactly what is going on (i literally just isolated this), but from the stack trace i’m guessing that me calling !=(_:_:) fell into some kind of infinite recursion.

EDIT: facepalm the default implementation of ==(_:_:), which the Equatable.!=(_:_:) operator calls, is accessing rawValue, which is calling itself with ==(_:_:)…

2 Likes
5

Yeah, you hit the not-quite-bug of the RawRepresentable ==…

6

Same bug as this?

I don't think it's right for EQ to compare rawValues instead of enumeration tags, we had a thread on this recently. As a workaround I'd suggest to always override "==" when you adding RawRepresentable conformance, in this case:

    public static func == (lhs: Self, rhs: Self) -> Bool {
        switch (lhs, rhs) {
            case (.a, .a), (.b, .b): true
            case (.a, .b), (.b, .a): false
        }
    }
2 Likes
7

except i’m naturally not thrilled to have to write this every time (and i, or the AI code generator, might make a typo), it really ought to be something the compiler can generate automatically. it’s regrettable that the synthesized Equatable conformance gets disabled when enums have raw types.

1 Like
8

Interestingly, this compiles and works fine (but obviously bad):

extension Bool: ExpressibleByIntegerLiteral {
    public init(integerLiteral value: Int) { fatalError("don't call") }
}

enum Verification: Bool {
    case again = false
    case debut = true
}

Well spotted. I wonder what is the intended use-case here.

2 Likes
9

Does it still call the RawRepresentable version of == if you move the RawRepresentable conformance to a separate file from the enum?