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

base/mac/foundation_util.h

Index: base/mac/foundation_util.h
diff --git a/base/mac/foundation_util.h b/base/mac/foundation_util.h
index 4c4abc69dbade923e49adf927d49fe3dcc4721e4..c9bb7dbe4a46100767a06928d3cdcc11a0c1d1f7 100644
--- a/base/mac/foundation_util.h
+++ b/base/mac/foundation_util.h
@@ -224,6 +224,39 @@ 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