Use initializer_list in ChromePermissionMessageRule ctors

chrome/common/extensions/permissions/chrome_permission_message_rules.h

 // Copyright 2014 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 CHROME_COMMON_EXTENSIONS_PERMISSIONS_CHROME_PERMISSION_MESSAGE_RULES_H_
 #define CHROME_COMMON_EXTENSIONS_PERMISSIONS_CHROME_PERMISSION_MESSAGE_RULES_H_
 
+#include <initializer_list>
 #include <set>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/linked_ptr.h"
 #include "extensions/common/permissions/api_permission.h"
 #include "extensions/common/permissions/api_permission_set.h"
 #include "extensions/common/permissions/permission_message.h"
 
 namespace extensions {
@@ skipping 44 matching lines @@
   static std::vector<ChromePermissionMessageRule> GetAllRules();
 
   std::set<APIPermission::ID> required_permissions() const;
   std::set<APIPermission::ID> optional_permissions() const;
   std::set<APIPermission::ID> all_permissions() const;
 
   PermissionMessage GetPermissionMessage(
       const PermissionIDSet& permissions) const;
 
  private:
-  class PermissionIDSetInitializer;
-
   // Create a rule using the default formatter (display the message with ID
   // |message_id|).
-  ChromePermissionMessageRule(int message_id,
-                              const PermissionIDSetInitializer& required,
-                              const PermissionIDSetInitializer& optional);
+  ChromePermissionMessageRule(
+      int message_id,
+      const std::initializer_list<APIPermission::ID>& required,
+      const std::initializer_list<APIPermission::ID>& optional);
   // Create a rule with a custom formatter. Takes ownership of |formatter|.
-  ChromePermissionMessageRule(ChromePermissionMessageFormatter* formatter,
-                              const PermissionIDSetInitializer& required,
-                              const PermissionIDSetInitializer& optional);
+  ChromePermissionMessageRule(
+      ChromePermissionMessageFormatter* formatter,
+      const std::initializer_list<APIPermission::ID>& required,
+      const std::initializer_list<APIPermission::ID>& optional);

[Marc Treib, 2016/11/30 14:42:52]

I'm not very familiar with initializer_lists yet - could all those just say
std::set<APIPermission::ID>& (effectively converting from initializer_list to
set one step earlier), to get rid of the somewhat ugly initializer_list type in
the signature?
Not a big deal though, especially since this is all private.

[tbarzic, 2016/11/30 18:35:44]

I was hoping to use std::set, too, but clang complains when {} is passed to the
constructor with error: "chosen constructor is explicit in copy-initialization"
(http://cplusplus.github.io/LWG/lwg-defects.html#2193 seems relevant).
I guess it could be worked around by passing std:set<>() instead of {}, but this
seems cleaner :)

 
   std::set<APIPermission::ID> required_permissions_;
   std::set<APIPermission::ID> optional_permissions_;
 
   // Owned by this class. linked_ptr is needed because this object is copyable
   // and stored in a returned vector.
   linked_ptr<ChromePermissionMessageFormatter> formatter_;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_PERMISSIONS_CHROME_PERMISSION_MESSAGE_RULES_H_