How to display OptionSet values in human-readable form?

Question

Swift has the OptionSet type, which basically adds set operations to C-Style bit flags. Apple is using them pretty extensively in their frameworks. Examples include the options

Answer 1

This article in NSHipster gives an alternative to OptionSet that offers all the features of an OptionSet, plus easy logging:

https://nshipster.com/optionset/

If you simply add a requirement that the Option type be CustomStringConvertible, you can log Sets of this type very cleanly. Below is the code from the NSHipster site - the only change being the addition of CustomStringConvertible conformance to the Option class

protocol Option: RawRepresentable, Hashable, CaseIterable, CustomStringConvertible {}

enum Topping: String, Option {
    case pepperoni, onions, bacon,
    extraCheese, greenPeppers, pineapple

    //I added this computed property to make the class conform to CustomStringConvertible
    var description: String {
        return ".\(self.rawValue)"
    }
}

extension Set where Element == Topping {
    static var meatLovers: Set {
        return [.pepperoni, .bacon]
    }

    static var hawaiian: Set {
        return [.pineapple, .bacon]
    }

    static var all: Set {
        return Set(Element.allCases)
    }
}

typealias Toppings = Set

extension Set where Element: Option {
    var rawValue: Int {
        var rawValue = 0
        for (index, element) in Element.allCases.enumerated() {
            if self.contains(element) {
                rawValue |= (1 << index)
            }
        }
        return rawValue
    }
}

Then using it:

let toppings: Set = [.onions, .bacon]

print("toppings = \(toppings), rawValue = \(toppings.rawValue)")

That outputs

toppings = [.onions, .bacon], rawValue = 6

Just like you want it to.

That works because a Set displays its members as a comma-delimited list inside square brackets, and uses the description property of each set member to display that member. The description property simply displays each item (the enum's name as a String) with a . prefix

And since the rawValue of a Set is the same as an OptionSet with the same list of values, you can convert between them readily.

I wish Swift would just make this a native language feature for OptionSets.