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

base/mac/foundation_util.mm

 // 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.
 
 #include "base/mac/foundation_util.h"
 
 #include <stdlib.h>
 #include <string.h>
 
 #include "base/file_path.h"
@@ skipping 330 matching lines @@
 CF_CAST_DEFN(CFBag);
 CF_CAST_DEFN(CFBoolean);
 CF_CAST_DEFN(CFData);
 CF_CAST_DEFN(CFDate);
 CF_CAST_DEFN(CFDictionary);
 CF_CAST_DEFN(CFNull);
 CF_CAST_DEFN(CFNumber);
 CF_CAST_DEFN(CFSet);
 CF_CAST_DEFN(CFString);
 
+#define GET_VAL_FROM_DICT_DEFN(TypeCF) \

[Mark Mentovai, 2011/11/11 23:20:45]

No reason to abbreviate here, you can write GET_VALUE_FROM_DICTIONARY_DEFN.

+template<> TypeCF##Ref \
+GetValueFromDictionary<TypeCF##Ref>(CFDictionaryRef dict, CFStringRef key) { \
+  CFTypeRef val = CFDictionaryGetValue(dict, key); \

[Mark Mentovai, 2011/11/11 23:20:45]

val and value as names are confusing.

+  TypeCF##Ref value = base::mac::CFCast<TypeCF##Ref>(val); \

[Mark Mentovai, 2011/11/11 23:20:45]

base::mac:: isn’t necessary, you’re already in that namespace.

+  if (!val) \
+    return value; \
+  if (!value) { \

[Mark Mentovai, 2011/11/11 23:20:45]

The contents of this block should be pulled out into its own
anonymous-namespaced helper function, so you’d write:

  if (!value) { \
    DLOG(WARNING) <<
        GetValueFromDictionaryErrorMessage(key, TypeCF##GetTypeID(), val); \
  } \
  return value; \

Why? Avoidance of duplication. You can write the function that produces the
error string in a totally type-independent way. You wind up only emitting one
copy of that code instead of ten, one for each flavor of this function that you
currently output.

+    ScopedCFTypeRef<CFStringRef> expected_type_ref( \
+        CFCopyTypeIDDescription(TypeCF##GetTypeID())); \
+    ScopedCFTypeRef<CFStringRef> actual_type_ref( \
+        CFCopyTypeIDDescription(CFGetTypeID(val))); \
+    DLOG(WARNING) << "Expected value for key " \
+                 << base::SysCFStringRefToUTF8(key) \

[Mark Mentovai, 2011/11/11 23:20:45]

The alignment’s all off here.

It’s off in the spot where you copied this from, too. Oops.

+                 << " to be " \
+                 << base::SysCFStringRefToUTF8(expected_type_ref) \
+                 << " but it was " \
+                 << base::SysCFStringRefToUTF8(actual_type_ref) \
+                 << " instead"; \
+    return NULL; \
+  } \
+  return value; \
+}

[Mark Mentovai, 2011/11/11 23:20:45]

You could write this entire function without any macros by putting something
like this into the header:

template<typename CFT>
CFT GetValueFromDictionary(CFDictionaryRef dict, CFStringRef key) {
  CFTypeRef value = CFDictionaryGetValue(dict, key);
  CFT value_specific = CFCast<CFT>(value);
  if (value && !value_specific) {
    DLOG(WARNING) << GetValueFromDictionaryErrorMessage(key, value);
  }
  return value_specific;
}

You lose the ability to have the error message show the expected type name, but
I think that’s fine. You can also go to a small bit of extra trouble to
templatize a function that can provide the type name.

+
+GET_VAL_FROM_DICT_DEFN(CFArray);
+GET_VAL_FROM_DICT_DEFN(CFBag);
+GET_VAL_FROM_DICT_DEFN(CFBoolean);
+GET_VAL_FROM_DICT_DEFN(CFData);
+GET_VAL_FROM_DICT_DEFN(CFDate);
+GET_VAL_FROM_DICT_DEFN(CFDictionary);
+GET_VAL_FROM_DICT_DEFN(CFNull);
+GET_VAL_FROM_DICT_DEFN(CFNumber);
+GET_VAL_FROM_DICT_DEFN(CFSet);
+GET_VAL_FROM_DICT_DEFN(CFString);
+
 }  // namespace mac
 }  // namespace base
 
 std::ostream& operator<<(std::ostream& o, const CFStringRef string) {
   return o << base::SysCFStringRefToUTF8(string);
 }
 
 std::ostream& operator<<(std::ostream& o, const CFErrorRef err) {
   base::mac::ScopedCFTypeRef<CFStringRef> desc(CFErrorCopyDescription(err));
   base::mac::ScopedCFTypeRef<CFDictionaryRef> user_info(
       CFErrorCopyUserInfo(err));
   CFStringRef errorDesc = NULL;
   if (user_info.get()) {
     errorDesc = reinterpret_cast<CFStringRef>(
         CFDictionaryGetValue(user_info.get(), kCFErrorDescriptionKey));
   }
   o << "Code: " << CFErrorGetCode(err)
     << " Domain: " << CFErrorGetDomain(err)
     << " Desc: " << desc.get();
   if(errorDesc) {
     o << "(" << errorDesc << ")";
   }
   return o;
 }