OrderedDictionary.swift

import Foundation

public struct OrderedDictionary<Tk: Hashable, Tv> : MutableCollectionType {
    var keys: Array<Tk> = []
    var values: Dictionary<Tk,Tv> = [:]
    
    public typealias Index = Int
    
    public var count: Int {
        return self.keys.count;
    }
    
    public var startIndex: Int {
        return self.keys.startIndex
    }
    
    public var endIndex: Int {
        return self.keys.endIndex
    }
    
    public init() {}
    
    public func generate() -> AnyGenerator<(Tk, Tv)> {
        var index = 0
        return anyGenerator {
            if index < self.keys.count {
                let key = self.keys[index]
                let value = self.values[key]!
                index += 1
                
                return (key, value)
            }
            return nil
        }
    }
    
    public subscript(index: Int) -> (Tk, Tv)? {
        get {
            let key = self.keys[index]
            
            return (key, self.values[key]!)
        }
        set(newValue) {
            let key = self.keys[index]
            self.values.removeValueForKey(key)
            
            if let value = newValue {
                self.keys[index] = value.0
                self.values[value.0] = value.1
            } else {
                self.keys.removeAtIndex(index)
            }
        }
    }
    
    public subscript(key: Tk) -> Tv? {
        get {
            return self.values[key]
        }
        set(newValue) {
            if newValue == nil {
                self.values.removeValueForKey(key)
                self.keys = self.keys.filter {$0 != key}
            }
            
            let oldValue = self.values.updateValue(newValue!, forKey: key)
            if oldValue == nil {
                self.keys.append(key)
            }
        }
    }
    
    public var description: String {
        var result = "{\n"
        for i in 0..<self.count {
            result += "[\(i)]: \(self.keys[i]) => \(self[i])\n"
        }
        result += "}"
        return result
    }
}