gistfile1.swift

/**
 * Map a function over the values of a map, returning only entries
 * for which the function returns non-nil. Works seamlessly with a
 * function that has a non-optional type signature, too.
 */
public func mapValues<K, T, U>(source: [K: T], f: (T -> U?)) -> [K: U] {
    var m = [K: U]()
    for (k, v) in source {
        if let u = f(v) {
            m[k] = u
        }
    }
    return m
}

…

    public static func mapFromJSON(map: [String: JSON]?) -> [String: EngineMeta]? {
        if map == nil {
            return nil
        }
        return mapValues(map!) { json in
            return EngineMeta.fromJSON(json)
        }
    }