Create ObjCCast<>() and ObjCCastStrict<>() methods

base/mac/foundation_util.h

 // Copyright (c) 2011 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_
 #pragma once
 
 #include <CoreFoundation/CoreFoundation.h>
 
@@ skipping 206 matching lines @@
 // CFStringRef some_string = base::mac::CFCastStrict<CFStringRef>(
 //     base::mac::GetValueFromDictionary(some_dict,
 //                                       CFSTR("a_key"),
 //                                       CFStringGetTypeID()));
 BASE_EXPORT template<class T>
 T CFCast(const CFTypeRef& cf_val);
 
 BASE_EXPORT template<class T>
 T CFCastStrict(const CFTypeRef& cf_val);
 
+#if defined(__OBJC__)
+
+// ObjCCast<>() and ObjCCastStrict<>() cast a basic id to a more
+// specific (NSObject-derived) type. The compatibility of the passed
+// object is found by checking if it's a kind of the requested type
+// identifier. If the supplied object is not compatible with the
+// requested return type, ObjCCast<>() returns NULL and

[Mark Mentovai, 2011/10/20 14:14:16]

Adjust the comment to reference nil instead of NULL as well.

+// ObjCCastStrict<>() will DCHECK. Providing a NULL pointer to either
+// variant results in NULL being returned without triggering any DCHECK.
+//
+// Example usage:
+// NSNumber* some_number = base::mac::ObjCCast<NSNumber>(
+//     [dict objectForKey:@"object"]);

[Mark Mentovai, 2011/10/20 14:14:16]

A good example for this would be:

NSString* version = base::mac::ObjCCast<NSString>([bundle
objectForInfoDictionaryKey:@"CFBundleShortVersionString"]);

(assuming bundle is an NSBundle*)

because the bundle’s Info.plist is not entirely within the program’s control,
and if some prankster puts a non-string into the plist for
CFBundleShortVersionString, the program might prefer to treat it the same as a
missing value rather than crashing.

+//
+// NSString* some_str = base::mac::ObjCCastStrict<NSString>(
+//     [ns_arr_of_ns_strs objectAtIndex:0]);
+BASE_EXPORT template<class T>
+T* ObjCCast(id objc_val) {
+  if ([objc_val isKindOfClass:[T class]]) {
+    return reinterpret_cast<T*>(objc_val);
+  }
+  return nil;
+}
+
+BASE_EXPORT template<class T>
+T* ObjCCastStrict(id objc_val) {
+  T* rv = ObjCCast<T>(objc_val);
+  DCHECK(objc_val == nil || rv);
+  return rv;
+}
+
+#endif  // defined(__OBJC__)
+
 }  // namespace mac
 }  // namespace base
 
 // Stream operations for CFTypes. They can be used with NSTypes as well
 // 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_