Using enums to define an API router where query params are defined in a trailing closure (updated for latest Swift)

api_router_swift_2.2.swift

// http://eliasbagley.github.io/json/api/alamofire/2015/09/25/making-network-requests-with-alamofire.html
enum APIRouter: URLRequestConvertible
{
    static let BASE_URL = "http://foo"
    static let API_KEY = "1231254"
    
    case User(Int, closure: () -> [String:AnyObject])
    case Likes(Int, Int)
    
    var URLRequest: NSMutableURLRequest
    {
        var path:String!
        var parameters:[String:AnyObject]
        
        switch(self) {
        case .User (let page, let closure):
            parameters = closure()
            path = "/user/\(page)"
        case .Likes(let id, let commentsPage):
            parameters = ["commentsPage":commentsPage]
            path = "/likes/\(id)/user"
        }
    
        let URL = NSURL(string: APIRouter.BASE_URL)
        let URLRequest = NSURLRequest(URL:URL!.URLByAppendingPathComponent(path))
        let encoding = Alamofire.ParameterEncoding.URL
        return encoding.encode(URLRequest, parameters: parameters).0
    }
}

// Example
let x = APIRouter.User(4) { ["this":"that"] }
print(x.URLRequest)   // -> URL: http://foo/user/4?this=that