Open Radar

 
Summary:
Often when I write code using the NSURLSession API, I initially write this:

    let config = NSURLSessionConfiguration()
    let session = NSURLSession(configuration: config, delegate: self, delegateQueue: nil)

When I write this, my expectation is that config will be a default session configuration. But this code crashes at runtime with an "unrecognized selector" error.

The correct code is

    let config = NSURLSessionConfiguration.defaultSessionConfiguration()

I find it surprising that calling the default (and only) constructor for NSURLSessionConfiguration results in an unusable instance. Some web searches indicate that other people have been similarly surprised.

I propose that the NSURLSessionConfiguration no-arg constructor be changed so that it produces the same result as defaultSessionConfiguration(). If that would have a bad effect on existing applications, then I propose that the no-arg constructor be deprecated (with a warning from Xcode when used) in favor of a new constructor that makes the intent explicit, like

    NSURLSessionConfiguration(usingDefaultConfiguration: bool)

Steps to Reproduce:
Paste the following into an OS X Swift Playground:

import Cocoa
import XCPlayground

XCPlaygroundPage.currentPage.needsIndefiniteExecution = true

// This should be "let config = NSURLSessionConfiguration.defaultSessionConfiguration()"
let config = NSURLSessionConfiguration()

let url = NSURL(string: "http://www.apple.com")!
let session = NSURLSession(configuration: config, delegate: nil, delegateQueue: nil)
let dataTask = session.dataTaskWithURL(url) { (data, response, error) in
    if let error = error {
        print("error: \(error.localizedDescription)")
    }
    else {
        print("Received response")
    }
}
dataTask.resume()


Expected Results:
Should see "Received response" printed.

Actual Results:
Playground displays "Execution was interrupted, reason signal SIGABRT", with this in the debug output:

2016-03-03 12:49:34.919 URLSessionPlayground[17149:566179] -[NSURLSessionConfiguration disposition]: unrecognized selector sent to instance 0x7f8900426750


This can be fixed by changing "NSURLSessionConfiguration()" to "NSURLSessionConfiguration.defaultSessionConfiguration()"

Version:
Xcode 7.2.1 (7C1002) and OS X 10.11.3 (15D21)

Notes:
This issue is described for the OS X SDK, where I have tested it, but I believe this also applies to the iOS and tvOS SDKs.