Swift 3 API parity: Change type of HTTPURLResponse.allHeaderFields to match Darwin

Author: Pushkar N Kulkarni

Foundation/NSURLResponse.swift

@@ -154,7 +154,7 @@ open class HTTPURLResponse : URLResponse {
     ///
     /// - Important: This is an *experimental* change from the
     /// `[NSObject: AnyObject]` type that Darwin Foundation uses.
-    public let allHeaderFields: [String: String]
+    public let allHeaderFields: [AnyHashable : Any]
 
     /// Convenience method which returns a localized string
     /// corresponding to the status code for this response.
@@ -233,7 +233,8 @@ open class HTTPURLResponse : URLResponse {
     /// This property is intended to produce readable output.
     override open var description: String {
         var result = "<\(type(of: self)) \(Unmanaged.passUnretained(self).toOpaque())> { URL: \(url!.absoluteString) }{ status: \(statusCode), headers {\n"
-        for(key, value) in allHeaderFields {
+        for(aKey, aValue) in allHeaderFields {
+            guard let key = aKey as? String, let value = aValue as? String else { continue } //shouldn't typically fail here 
             if((key.lowercased() == "content-disposition" && suggestedFilename != "Unknown") || key.lowercased() == "content-type") {
                 result += "   \"\(key)\" = \"\(value)\";\n"
             } else {

TestFoundation/TestNSURLResponse.swift

@@ -156,8 +156,8 @@ class TestNSHTTPURLResponse : XCTestCase {
         let f = ["A": "1", "B": "2"]
         let sut = HTTPURLResponse(url: url, statusCode: 200, httpVersion: "HTTP/1.1", headerFields: f)
         XCTAssertEqual(sut?.allHeaderFields.count, 2)
-        XCTAssertEqual(sut?.allHeaderFields["A"], "1")
-        XCTAssertEqual(sut?.allHeaderFields["B"], "2")
+        XCTAssertEqual(sut?.allHeaderFields["A"] as! String, "1")
+        XCTAssertEqual(sut?.allHeaderFields["B"] as! String, "2")
     }
 
     // Note that the message content length is different from the message