Add unit tests for swift 4 mode

Author: phausler

test/stdlib/TestData_Swift4.swift

@@ -0,0 +1,35 @@
+
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -swift-version 4 %s -o %t/TestData_Swift4
+// RUN: %target-run %t/TestData_Swift4
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+import Foundation
+import StdlibUnittest
+
+var DataTests = TestSuite("TestDataSwift4")
+
+DataTests.test("functional map init usage") {
+	let res1 = [[UInt8(0), UInt8(1), UInt8(2)]].map(Data.init) // previously this could be done without being ambiguous (however in swift 4.2 an overload was added that makes it ambiguous as a function ref)
+	// the following two strategies are preferred to the previous version
+	let res2 = [[UInt8(0), UInt8(1), UInt8(2)]].map(Data.init(_:))
+	let res3 = [[UInt8(0), UInt8(1), UInt8(2)]].map { Data($0) }
+
+	expectEqual(res1.count, 1)
+	expectEqual(res2.count, 1)
+	expectEqual(res3.count, 1)
+
+	expectEqual(res1[0], res2[0])
+	expectEqual(res2[0], res3[0])
+}
+
+runAllTests()