Fix Data(capacity:) and Data(count:) to return non-optional (#538)

- This matches the Foundation API in Darwin

Author: spevans

Foundation/Data.swift

@@ -217,12 +217,18 @@ public struct Data : ReferenceConvertible, CustomStringConvertible, Equatable, H
 
     /// Initialize a `Data` with the specified size.
     ///
+    /// This initializer doesn't necessarily allocate the requested memory right away. `Data` allocates additional memory as needed, so `capacity` simply establishes the initial capacity. When it does allocate the initial memory, though, it allocates the specified amount.
+    ///
+    /// This method sets the `count` of the data to 0.
+    ///
+    /// If the capacity specified in `capacity` is greater than four memory pages in size, this may round the amount of requested memory up to the nearest full page.
+    ///
     /// - parameter capacity: The size of the data.
-    public init?(capacity: Int) {
+    public init(capacity: Int) {
         if let d = NSMutableData(capacity: capacity) {
             _wrapped = _SwiftNSData(immutableObject: d)
         } else {
-            return nil
+            fatalError("Unable to allocate data of the requested capacity")
         }
     }
 
@@ -281,11 +287,11 @@ public struct Data : ReferenceConvertible, CustomStringConvertible, Equatable, H
     /// Initialize a `Data` with the specified count of zeroed bytes.
     ///
     /// - parameter count: The number of bytes the data initially contains.
-    public init?(count: Int) {
+    public init(count: Int) {
         if let memory = calloc(1, count)?.bindMemory(to: UInt8.self, capacity: count) {
             self.init(bytesNoCopy: memory, count: count, deallocator: .free)
         } else {
-            return nil
+            fatalError("Unable to allocate data of the requested count")
         }
     }
 

Foundation/NSString.swift

@@ -844,20 +844,18 @@ extension NSString {
         if convertedLen != len {
             return nil 	// Not able to do it all...
         }
-        
-        var data = Data(count: reqSize)
-        if data != nil {
-            if 0 < reqSize {
-                data!.count = data!.withUnsafeMutableBytes { (mutableBytes: UnsafeMutablePointer<UInt8>) -> Int in
-                    if __CFStringEncodeByteStream(_cfObject, 0, len, true, cfStringEncoding, lossy ? (encoding == String.Encoding.ascii.rawValue ? 0xFF : 0x3F) : 0, UnsafeMutablePointer<UInt8>(mutableBytes), reqSize, &reqSize) == convertedLen {
-                        return reqSize
-                    } else {
-                        fatalError("didn't convert all characters")
-                    }
-                }
 
-                return data
+        if 0 < reqSize {
+            var data = Data(count: reqSize)
+            data.count = data.withUnsafeMutableBytes { (mutableBytes: UnsafeMutablePointer<UInt8>) -> Int in
+                if __CFStringEncodeByteStream(_cfObject, 0, len, true, cfStringEncoding, lossy ? (encoding == String.Encoding.ascii.rawValue ? 0xFF : 0x3F) : 0, UnsafeMutablePointer<UInt8>(mutableBytes), reqSize, &reqSize) == convertedLen {
+                    return reqSize
+                } else {
+                    fatalError("didn't convert all characters")
+                }
             }
+
+            return data
         }
         return nil
     }
@@ -1145,7 +1143,7 @@ extension NSString {
                 NSURLErrorKey: dest,
             ])
         }
-        var mData = Data(count: numBytes)!
+        var mData = Data(count: numBytes)
         // The getBytes:... call should hopefully not fail, given it succeeded above, but check anyway (mutable string changing behind our back?)
         var used = 0
         // This binds mData memory to UInt8 because Data.withUnsafeMutableBytes does not handle raw pointers.

TestFoundation/TestNSData.swift

@@ -42,7 +42,8 @@ class TestNSData: XCTestCase {
             ("test_rangeOfData",test_rangeOfData),
             ("test_initMutableDataWithLength", test_initMutableDataWithLength),
             ("test_replaceBytes", test_replaceBytes),
-            ("test_initDataWithCount", test_initDataWithCount)
+            ("test_initDataWithCapacity", test_initDataWithCapacity),
+            ("test_initDataWithCount", test_initDataWithCount),
         ]
     }
 
@@ -378,12 +379,14 @@ class TestNSData: XCTestCase {
         XCTAssertEqual(mData, expected)
     }
 
+    func test_initDataWithCapacity() {
+        let data = Data(capacity: 123)
+        XCTAssertEqual(data.count, 0)
+    }
+
     func test_initDataWithCount() {
         let dataSize = 1024
-        guard let data = Data(count: dataSize) else {
-            XCTFail("Could not create zeroed data")
-            return
-        }
+        let data = Data(count: dataSize)
         XCTAssertEqual(data.count, dataSize)
         if let index = (data.index { $0 != 0 }) {
             XCTFail("Byte at index: \(index) is not zero: \(data[index])")

TestFoundation/TestNSJSONSerialization.swift

@@ -787,7 +787,7 @@ extension TestNSJSONSerialization {
     func test_jsonObjectToOutputStreamFile() {
         let dict = ["a":["b":1]]
         do {
-            let filePath = createTestFile("TestFileOut.txt",_contents: Data(capacity: 128)!)
+            let filePath = createTestFile("TestFileOut.txt",_contents: Data(capacity: 128))
             if filePath != nil {
                 let outputStream = NSOutputStream(toFileAtPath: filePath!, append: true)
                 outputStream?.open()

TestFoundation/TestNSStream.swift

@@ -125,7 +125,7 @@ class TestNSStream : XCTestCase {
     }
 
     func test_outputStreamCreationToFile() {
-        let filePath = createTestFile("TestFileOut.txt", _contents: Data(capacity: 256)!)
+        let filePath = createTestFile("TestFileOut.txt", _contents: Data(capacity: 256))
         if filePath != nil {
             let outputStream = NSOutputStream(toFileAtPath: filePath!, append: true)
             XCTAssertEqual(Stream.Status.notOpen, outputStream!.streamStatus)
@@ -159,7 +159,7 @@ class TestNSStream : XCTestCase {
     }
 
     func test_outputStreamCreationWithUrl() {
-        let filePath = createTestFile("TestFileOut.txt", _contents: Data(capacity: 256)!)
+        let filePath = createTestFile("TestFileOut.txt", _contents: Data(capacity: 256))
         if filePath != nil {
             let outputStream = NSOutputStream(url: URL(fileURLWithPath: filePath!), append: true)
             XCTAssertEqual(Stream.Status.notOpen, outputStream!.streamStatus)