Implementing get Requests with swift

REST.swift

//
//  REST.swift
//  CoconutTests
//
//  Created by Andre Oriani on 2/5/16.
//  Copyright © 2016 Walmartlabs. All rights reserved.
//

import Foundation

class RestManager {
    private let session = NSURLSession(
        configuration: NSURLSessionConfiguration.defaultSessionConfiguration(),
        delegate:nil,
        delegateQueue:NSOperationQueue.mainQueue()
    )
    
    private func performRequest<ResponseType: Decodable>(request:NSURLRequest,
        success: (ResponseType) ->Void = {_ in },
        failure: () -> Void = {}) -> NSURLSessionDataTask {
            let task : NSURLSessionDataTask = session.dataTaskWithRequest(request,
                completionHandler: { (data, response, error) in
                    guard let response = response as? NSHTTPURLResponse else {failure(); return}
                    if (error == nil) && (200..<300 ~= response.statusCode) {
                        guard let data = data else {failure(); return}
                        do {
                            let json = JSON(data: data)
                            let model = try ResponseType.decode(json)
                            success(model)
                        } catch {
                            failure()
                        }
                        
                    } else {
                        failure()
                    }
                    
                })
            task.resume()
            return task
    }
    
    func getPopular(success: (Payload)-> Void) -> NSURLSessionDataTask {
        let clientId = "e05c462ebd86446ea48a5af73769b602"
        let url = NSURL(string:"https://api.instagram.com/v1/media/popular?client_id=\(clientId)")
        let request = NSURLRequest(URL: url!)
        return performRequest(request, success: success)
    }
}