swift CollectionType extension to map any collection to a dictionary

toDictionary.swift

extension CollectionType {
    @warn_unused_result
    func toDictionary<K, V>
        (@noescape transform:(element: Self.Generator.Element) -> (key: K, value: V)?) -> [K : V] {
            return self.reduce([:]) { (var dictionary, e) in
                if let (key, value) = transform(element: e){
                    dictionary[key] = value
                }
                return dictionary
            }
    }
}