Use variadic template for screen handler's AddCallback.

components/login/base_screen_handler_utils.h

 // Copyright (c) 2013 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 COMPONENTS_LOGIN_BASE_SCREEN_HANDLER_UTILS_H_
 #define COMPONENTS_LOGIN_BASE_SCREEN_HANDLER_UTILS_H_
 
 #include <cstddef>
 #include <string>
 
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/strings/string16.h"
+#include "base/tuple.h"
 #include "base/values.h"
 #include "components/login/login_export.h"
 
 namespace login {
 
 typedef std::vector<std::string> StringList;
 typedef std::vector<base::string16> String16List;
 
 template <typename T>
 struct LOGIN_EXPORT UnwrapConstRef {
@@ skipping 28 matching lines @@
 base::FundamentalValue LOGIN_EXPORT MakeValue(int v);
 base::FundamentalValue LOGIN_EXPORT MakeValue(double v);
 base::StringValue LOGIN_EXPORT MakeValue(const std::string& v);
 base::StringValue LOGIN_EXPORT MakeValue(const base::string16& v);
 
 template <typename T>
 inline const T& MakeValue(const T& v) {
   return v;
 }
 
-void LOGIN_EXPORT CallbackWrapper0(base::Callback<void()> callback,
-                                   const base::ListValue* args);
-
-template <typename A1>
-void CallbackWrapper1(base::Callback<void(A1)> callback,
-                      const base::ListValue* args) {
-  DCHECK(args);
-  DCHECK_EQ(1u, args->GetSize());
-  typename UnwrapConstRef<A1>::Type arg1;
-  if (!GetArg(args, 0, &arg1)) {
-    NOTREACHED();
-    return;
-  }
-  callback.Run(arg1);
+template <typename Arg, size_t index>
+typename UnwrapConstRef<Arg>::Type ParseArg(const base::ListValue* args) {
+  typename UnwrapConstRef<Arg>::Type parsed;
+  CHECK(GetArg(args, index, &parsed));
+  return parsed;
 }
 
-template <typename A1, typename A2>
-void CallbackWrapper2(base::Callback<void(A1, A2)> callback,
-                      const base::ListValue* args) {
+template <typename... Args, size_t... Ns>
+inline void DispatchToCallback(const base::Callback<void(Args...)>& callback,
+                               const base::ListValue* args,
+                               IndexSequence<Ns...> indexes) {
   DCHECK(args);
-  DCHECK_EQ(2u, args->GetSize());
-  typename UnwrapConstRef<A1>::Type arg1;
-  typename UnwrapConstRef<A2>::Type arg2;
-  if (!GetArg(args, 0, &arg1) || !GetArg(args, 1, &arg2)) {
-    NOTREACHED();
-    return;
-  }
-  callback.Run(arg1, arg2);
+  DCHECK_EQ(sizeof...(Args), args->GetSize());
+
+  callback.Run(ParseArg<Args, Ns>(args)...);
 }
 
-template <typename A1, typename A2, typename A3>
-void CallbackWrapper3(base::Callback<void(A1, A2, A3)> callback,
-                      const base::ListValue* args) {
-  DCHECK(args);
-  DCHECK_EQ(3u, args->GetSize());
-  typename UnwrapConstRef<A1>::Type arg1;
-  typename UnwrapConstRef<A2>::Type arg2;
-  typename UnwrapConstRef<A3>::Type arg3;
-  if (!GetArg(args, 0, &arg1) || !GetArg(args, 1, &arg2) ||
-      !GetArg(args, 2, &arg3)) {
-    NOTREACHED();
-    return;
-  }
-  callback.Run(arg1, arg2, arg3);
+template <typename... Args>
+void CallbackWrapper(const base::Callback<void(Args...)>& callback,
+                     const base::ListValue* args) {
+  DispatchToCallback(callback, args, MakeIndexSequence<sizeof...(Args)>());
 }
 
-template <typename A1, typename A2, typename A3, typename A4>
-void CallbackWrapper4(base::Callback<void(A1, A2, A3, A4)> callback,
-                      const base::ListValue* args) {
-  DCHECK(args);
-  DCHECK_EQ(4u, args->GetSize());
-  typename UnwrapConstRef<A1>::Type arg1;
-  typename UnwrapConstRef<A2>::Type arg2;
-  typename UnwrapConstRef<A3>::Type arg3;
-  typename UnwrapConstRef<A4>::Type arg4;
-  if (!GetArg(args, 0, &arg1) || !GetArg(args, 1, &arg2) ||
-      !GetArg(args, 2, &arg3) || !GetArg(args, 3, &arg4)) {
-    NOTREACHED();
-    return;
-  }
-  callback.Run(arg1, arg2, arg3, arg4);
-}
-
-template <typename A1, typename A2, typename A3, typename A4, typename A5>
-void CallbackWrapper5(base::Callback<void(A1, A2, A3, A4, A5)> callback,
-                      const base::ListValue* args) {
-  DCHECK(args);
-  DCHECK_EQ(5u, args->GetSize());
-  typename UnwrapConstRef<A1>::Type arg1;
-  typename UnwrapConstRef<A2>::Type arg2;
-  typename UnwrapConstRef<A3>::Type arg3;
-  typename UnwrapConstRef<A4>::Type arg4;
-  typename UnwrapConstRef<A5>::Type arg5;
-  if (!GetArg(args, 0, &arg1) || !GetArg(args, 1, &arg2) ||
-      !GetArg(args, 2, &arg3) || !GetArg(args, 3, &arg4) ||
-      !GetArg(args, 4, &arg5)) {
-    NOTREACHED();
-    return;
-  }
-  callback.Run(arg1, arg2, arg3, arg4, arg5);
-}
 
 }  // namespace login
 
 #endif  // COMPONENTS_LOGIN_BASE_SCREEN_HANDLER_UTILS_H_