In Objective C, I follow the steps as outlined here and it works fine: https://developer.salesforce.com/docs/atlas.en-us.noversion.mobile_sdk.meta/mobile_sdk/ios_rest_apis_using_methods.htm?search_text=forceios

But when following the same steps translating the code into Swift, I run into an issue with the SFRestRequest initializer, whose signature is below:
 

Public convenience init(method: SFRestMethod, path: String, queryParams: [String : String]?)

As you can see, queryParams takes a Swift Dictionary with a key and value of the String type.  But when you follow the example, it seems you end up with a Dictionary with a key of the String type and value of the Dictionary type; and thus we have a type mismatch.

This doesn't seem to be a problem in Objective C, because upon inspection of the method signature in SFRestRequest.m, queryParams appears to be able to take a generic NSDictionary: 
 

+ (instancetype)requestWithMethod:(SFRestMethod)method path:(NSString *)path queryParams:(NSDictionary *)queryParams

For reference here is the Swift code I'm trying out:
 

//build the queryParams dictionary from a JSON String
let body: String = "{ \"body\" :{\"messageSegments\" :[{ \"type\" : \"Text\",\"text\" : \"My Comment\"}]}}"
        let queryParams = SFJsonUtils.objectFromJSONString(body) as! [String:AnyObject] 
//construct and send the request
        let request = SFRestRequest(method: SFRestMethod.POST, path: "/services/data/v36.0/connect/communities/my_community_ID/chatter/feed-elements/my_element_ID/capabilities/comments/items", queryParams: queryParams as? [String:String])
        SFRestAPI.sharedInstance().send(request, delegate: self)

But unwrapping queryParams fails and resolves to nil.  Trying to forcefully cast queryParams to [String:String] does not work either, and just causes a crash.

How might I get around this?