Raw type 'Bool' is not expressible by any literal

问题

I want to have my enums easily compatible with @IBInspectable, so for the sake of simplicity, I tried to have it representable with type Bool:

enum TopBarStyle: Bool {
    case darkOnLight
    case lightOnDark
}

But Xcode is giving me:

Raw type 'Bool' is not expressible by any literal

That's strange, as true and false seem to be perfect candidates for expressibility by literals.

I've also tried to add RawRepresentable conformance to type Bool with:

extension Bool: RawRepresentable {
    public init?(rawValue: Bool) {
        self = rawValue
    }
    public var rawValue: Bool {
        get { return self }
    }
}

But it didn't solve the error.

回答1:

I don't think this is necessary. You can just make a normal enum and then switch over its cases. Also, it's not clear at all what TopBarStyle(rawValue: true) would mean if this could be achieved.

I would either use var darkOnLight: Bool, or enum TopBarStyle { /*cases*/ } and switch over the cases as necessary.

回答2:

Swift 3 natively defines those nine literal representations:

ExpressibleByNilLiteral (nil)
ExpressibleByBooleanLiteral (false)
ExpressibleByArrayLiteral ([])
ExpressibleByDictionaryLiteral ([:])
ExpressibleByIntegerLiteral (0)
ExpressibleByFloatLiteral (0.0)
ExpressibleByUnicodeScalarLiteral ("\u{0}")
ExpressibleByExtendedGraphemeClusterLiteral ("\u{0}")
ExpressibleByStringLiteral ("")

But enum raw representation will apparently only accept natively the subset of those representions that start with a digit (0-9), a sign (-, +) or a quote ("): the last five protocols of above list.

In my opinion, the error message should have been more specific. Maybe something explicit like that would have been nice:

Raw type 'Bool' is not expressible by any numeric or quoted-string literal

Extending Bool to conform to one of those protocols is still possible, for example:

extension Bool: ExpressibleByIntegerLiteral {
    public init(integerLiteral value: Int) {
        self = value != 0
    }
}

And after doing so, this code now builds fine:

enum TopBarStyle: Bool {
    case darkOnLight
    case lightOnDark
}

@IBInspectable var style = TopBarStyle(rawValue: false)!

回答3:

my solution on swift 3

enum DataType: RawRepresentable {
    case given
    case received

    typealias RawValue = Bool
    var rawValue: RawValue {
        return self == .given ? true : false
    }
    init?(rawValue: RawValue) {
        self = rawValue == true ? .given : .received
    }
}

回答4:

Simplify your life:

enum TopBarStyle {
    case darkOnLight
    case lightOnDark

    var bool: Bool {
        switch self {
        case .darkOnLight:
            return true
        default:
            return false
        }
    }
}

Use as usual:

    var current = TopBarStyle.darkOnLight

    if current.bool {
        // do this
    } else {
        // do that
    }

You can extend cases to more but they are not reversible since its an N : 2 matrix

来源：https://stackoverflow.com/questions/42292197/raw-type-bool-is-not-expressible-by-any-literal

标签

swift

enums

rawrepresentable