Forward-declare enums in a way that is compatible with NS_ENUM

base/mac/foundation_util.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_MAC_FOUNDATION_UTIL_H_
 #define BASE_MAC_FOUNDATION_UTIL_H_
 
 #include <CoreFoundation/CoreFoundation.h>
 
 #include <string>
@@ skipping 10 matching lines @@
 class NSBundle;
 class NSString;
 #endif  // __OBJC__
 
 #if defined(OS_IOS)
 #include <CoreText/CoreText.h>
 #else
 #include <ApplicationServices/ApplicationServices.h>
 #endif
 
+// Adapted from NSObjCRuntime.h NS_ENUM definition (used in Foundation starting
+// with the OS X 10.8 SDK and the iOS 6.0 SDK).
+#if __has_extension(cxx_strong_enums) && \
+    (defined(OS_IOS) || (defined(MAC_OS_X_VERSION_10_8) && \
+                         MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_8))
+#define CR_FORWARD_ENUM(_type, _name) enum _name : _type _name
+#else
+#define CR_FORWARD_ENUM(_type, _name) _type _name
+#endif
+
 // Adapted from NSPathUtilities.h and NSObjCRuntime.h.
 #if __LP64__ || NS_BUILD_32_LIKE_64
-typedef unsigned long NSSearchPathDirectory;
+typedef CR_FORWARD_ENUM(unsigned long, NSSearchPathDirectory);
 typedef unsigned long NSSearchPathDomainMask;
 #else
-typedef unsigned int NSSearchPathDirectory;
+typedef CR_FORWARD_ENUM(unsigned int, NSSearchPathDirectory);
 typedef unsigned int NSSearchPathDomainMask;
 #endif
 
 typedef struct OpaqueSecTrustRef* SecACLRef;
 typedef struct OpaqueSecTrustedApplicationRef* SecTrustedApplicationRef;
 
 namespace base {
 
 class FilePath;
 
@@ skipping 303 matching lines @@
 // by using the NSToCFCast methods above.
 // e.g. LOG(INFO) << base::mac::NSToCFCast(@"foo");
 // Operator << can not be overloaded for ObjectiveC types as the compiler
 // can not distinguish between overloads for id with overloads for void*.
 BASE_EXPORT extern std::ostream& operator<<(std::ostream& o,
                                             const CFErrorRef err);
 BASE_EXPORT extern std::ostream& operator<<(std::ostream& o,
                                             const CFStringRef str);
 
 #endif  // BASE_MAC_FOUNDATION_UTIL_H_