I am using AFNetworking in my iOS app and for all the GET requests it makes, I build the url from a base URL and than add parameters using NSDictionary Key-Value pairs.
I guess u just have to do something like this:
let params = ["id" : [1, 2, 3, 4], ...];
which will be encoded into: ....id%5B%5D=1&id%5B%5D=2&id%5B%5D=3&id%5B%5D=4....