Create a nicer interface for base::mac::GetValueFromDictionary

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 f7821de08cdb09bca58aaca59da82bd689407e29..5f1b5800eb45370dddba2d97e3572074a2f8ee26 100644
--- a/base/mac/foundation_util.h
+++ b/base/mac/foundation_util.h
@@ -13,6 +13,7 @@
 
 #include "base/base_export.h"
 #include "base/logging.h"
+#include "base/mac/scoped_cftyperef.h"
 
 #if defined(__OBJC__)
 #import <Foundation/Foundation.h>
@@ -96,8 +97,31 @@ BASE_EXPORT FilePath GetUserLibraryPath();
 //   returns - path to the application bundle, or empty on error
 BASE_EXPORT FilePath GetAppBundlePath(const FilePath& exec_name);
 
+#define TYPE_NAME_FOR_CF_TYPE_DECL(TypeCF) \
+std::string TypeNameForCFType(TypeCF##Ref);
+
+TYPE_NAME_FOR_CF_TYPE_DECL(CFArray);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFBag);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFBoolean);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFData);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFDate);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFDictionary);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFNull);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFNumber);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFSet);
+TYPE_NAME_FOR_CF_TYPE_DECL(CFString);
+
+#undef TYPE_NAME_FOR_CF_TYPE_DECL
+
+// Helper function for GetValueFromDictionary to create the error message
+// that appears when a type mismatch is encountered.
+std::string GetValueFromDictionaryErrorMessage(
+    CFStringRef key, const std::string& expected_type, CFTypeRef value);
+
 // Utility function to pull out a value from a dictionary, check its type, and
 // return it.  Returns NULL if the key is not present or of the wrong type.
+// This is now deprecated in favor of the two-argument form below.
+// TODO(kushi.p)

[Mark Mentovai, 2011/11/14 22:11:37]

Please finish this comment by referencing your newly-filed bug and saying what
the TODO means.

Reference:
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Castin...

Further reference:
https://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thr...

 BASE_EXPORT CFTypeRef GetValueFromDictionary(CFDictionaryRef dict,
                                              CFStringRef key,
                                              CFTypeID expected_type);
@@ -198,6 +222,9 @@ CF_TO_NS_CAST_DECL(CFWriteStream, NSOutputStream);
 CF_TO_NS_MUTABLE_CAST_DECL(String);
 CF_TO_NS_CAST_DECL(CFURL, NSURL);
 
+#undef CF_TO_NS_CAST_DECL
+#undef CF_TO_NS_MUTABLE_CAST_DECL

[Mark Mentovai, 2011/11/14 22:13:21]

I said three, right?

How about OBJC_CPP_CLASS_DECL?

[KushalP, 2011/11/14 22:20:47]

Ah, thought you just mean this 10 line block here.

+
 namespace base {
 namespace mac {
 
@@ -218,10 +245,10 @@ namespace mac {
 //     base::mac::GetValueFromDictionary(some_dict,
 //                                       CFSTR("a_key"),
 //                                       CFStringGetTypeID()));
-BASE_EXPORT template<class T>
+BASE_EXPORT template<typename T>
 T CFCast(const CFTypeRef& cf_val);
 
-BASE_EXPORT template<class T>
+BASE_EXPORT template<typename T>
 T CFCastStrict(const CFTypeRef& cf_val);
 
 #if defined(__OBJC__)
@@ -248,7 +275,7 @@ T CFCastStrict(const CFTypeRef& cf_val);
 //
 // NSString* str = base::mac::ObjCCastStrict<NSString>(
 //     [ns_arr_of_ns_strs objectAtIndex:0]);
-BASE_EXPORT template<class T>
+BASE_EXPORT template<typename T>
 T* ObjCCast(id objc_val) {
   if ([objc_val isKindOfClass:[T class]]) {
     return reinterpret_cast<T*>(objc_val);
@@ -256,7 +283,7 @@ T* ObjCCast(id objc_val) {
   return nil;
 }
 
-BASE_EXPORT template<class T>
+BASE_EXPORT template<typename T>
 T* ObjCCastStrict(id objc_val) {
   T* rv = ObjCCast<T>(objc_val);
   DCHECK(objc_val == nil || rv);
@@ -265,6 +292,23 @@ T* ObjCCastStrict(id objc_val) {
 
 #endif  // defined(__OBJC__)
 
+// Utility function to pull out a value from a dictionary, check its type, and
+// return it.  Returns NULL if the key is not present or of the wrong type.
+BASE_EXPORT template<typename T>
+T GetValueFromDictionary(CFDictionaryRef dict, CFStringRef key) {
+  CFTypeRef value = CFDictionaryGetValue(dict, key);
+  T value_specific = CFCast<T>(value);
+
+  if (value && !value_specific) {
+    std::string expected_type = TypeNameForCFType(value_specific);
+    DLOG(WARNING) << GetValueFromDictionaryErrorMessage(key,
+                                                        expected_type,
+                                                        value);
+  }
+
+  return value_specific;
+}
+
 }  // namespace mac
 }  // namespace base