Enumerating enum values – a universal approach

Universe-crashes.swift

// This new version seems to be syntactically correct,
// but it crashes together with Xcode as of beta 3. 
// (radar link should appear here)

// Find smallest N such that f(N) = nil.
func exhaust<T>(fun: Int -> T?) -> Int {
    var index = 0
    while fun(index) { index++ }
    return index
}

// Everything we can get from a mapping function.
struct Universe<Enum:RawRepresentable where Enum.RawType == Int>: Sequence {
    
    typealias MapType = MapSequenceView<Range<Int>, Enum>
    
    let fun:   Int -> Enum?    
    let count: Int
    let keys:  Range<Int>
    let values:MapType
    let pairs: Zip2<Range<Int>, MapType>
    
    init() {
        fun    = Enum.fromRaw
        count  = exhaust(fun)
        keys   = 0..<count
        values = map(keys, {Enum.fromRaw($0)!})        
        pairs  = Zip2(keys, values)
    }
    
    subscript(raw:Int) -> Enum {
        return fun(raw)!
    }
    
    func generate() ->  ZipGenerator2< RangeGenerator<Int>, MapType.GeneratorType> {
        return pairs.generate()
    } 
}

// Declare enum as usual and a helper structure.
enum Color: Int {
    case Red
    case Green 
    case Blue
}

let Colors = Universe<Color>()

// Enjoy.
for (index, color) in Colors {
    println("\(index) ⇒ \(color)")
}

for color in Colors.values {
    // ...
}

Color.Red == Colors[0]

Universe.swift

// Find smallest N such that f(N) = nil.
func exhaust<T>(fun: Int -> T?) -> Int {
    var index = 0
    while fun(index) { index++ }
    return index
}

// Everything we can get from a mapping function.
struct Universe<Enum>: Sequence {
    
    typealias MapType = MapSequenceView<Range<Int>, Enum>
    
    let fun:   Int -> Enum?    
    let count: Int
    let keys:  Range<Int>
    let values:MapType
    let pairs: Zip2<Range<Int>, MapType>
    
    init(_ enumf:Int -> Enum?) {
        fun    = enumf
        count  = exhaust(fun)
        keys   = 0..<count
        values = map(keys, {enumf($0)!})        
        pairs  = Zip2(keys, values)
    }
    
    subscript(raw:Int) -> Enum {
        return fun(raw)!
    }
    
    func generate() ->  ZipGenerator2< RangeGenerator<Int>, MapType.GeneratorType> {
        return pairs.generate()
    } 
}

// Declare enum as usual and a helper structure.
enum Color: Int {
    case Red
    case Green 
    case Blue
}

let Colors = Universe(Color.fromRaw)

// Enjoy.
for (index, color) in Colors {
    println("\(index) ⇒ \(color)")
}

for color in Colors.values {
    // enum values
}

Color.Red == Colors[0]   // true