SwiftSet.swift

struct MySet<KeyType : Hashable> : Sequence, ArrayLiteralConvertible
{
    var dictionaryOfItems = Dictionary<KeyType,Bool>()
    typealias GeneratorType = MapSequenceGenerator<Dictionary<KeyType, Bool>.GeneratorType, KeyType>
    
    init() {}
    init(array: KeyType[]) {
        for item in array {
            self.dictionaryOfItems.updateValue(true, forKey: item)
        }
    }
    
    mutating
    func addObject(item:KeyType) -> Void {
        self.dictionaryOfItems.updateValue(true, forKey: item)
    }
    
    func containsObject(item:KeyType) -> Bool {
        return self.dictionaryOfItems[item].getLogicValue()
    }
    
    func generate() -> GeneratorType {
        return dictionaryOfItems.keys.generate()
    }
    
    static func convertFromArrayLiteral (elements: KeyType...) -> MySet<KeyType> {
        return MySet (array: elements)
    }
}

// the ArrayLiteralConvertible lets you do
let set : MySet<Int> = [1,2,3]

Cool. A clear improvement. I don't understand the reason for "Map" in MapSequenceGenerator, or how it relates to the DictionaryGenerator.

A little worrying how reifying all these abstractions into types is quickly producing Java-esque names for things, like three car pile-ups of abstract nouns, instead of the sanity of Cocoa. We'll see how it goes..