Use variadic template in media::BindToCurrentLoop()

media/base/bind_to_current_loop.h

-// This file was GENERATED by command:
-//     pump.py bind_to_current_loop.h.pump
-// DO NOT EDIT BY HAND!!!
-
-
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Copyright (c) 2015 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 MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_
 #define MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 20 matching lines @@
 T& TrampolineForward(T& t) { return t; }
 
 template <typename T, typename R>
 base::internal::PassedWrapper<scoped_ptr<T, R> > TrampolineForward(
     scoped_ptr<T, R>& p) { return base::Passed(&p); }
 
 template <typename T>
 base::internal::PassedWrapper<ScopedVector<T> > TrampolineForward(
     ScopedVector<T>& p) { return base::Passed(&p); }
 
-template <typename T> struct TrampolineHelper;
+template <typename Sig> struct TrampolineHelper;

[xhwang, 2015/03/05 17:19:15]

Is this needed here? Can we drop this line?

[xhwang, 2015/03/05 17:19:15]

What does "sig" mean here?

[wdzierzanowski, 2015/03/05 20:45:16]

We can't, the compiler doesn't like that:

../../media/base/bind_to_current_loop.h:43:8: error: explicit specialization of
non-template struct 'TrampolineHelper'

(where line 43 is the current 45)

I think the switch to a variadic template in the specialization doesn't remove
the reason this forward declaration was put here in the first place. And the
reason is the same as in the case of base::Callback: We first tell the compiler
TrampolineHelper is a struct template with one type parameter, and then define
specializations where the type is a function returning void and taking zero or
more arguments.

Should I add a comment explaining this? Or put a reference to base::Callback?

[wdzierzanowski, 2015/03/05 20:45:16]

It stands for "signature", and my intention was to align with the forward
declaration of base::Callback. I can change it to Signature, or just revert to
T.

[xhwang, 2015/03/05 20:48:49]

A comment would help, thanks!

[wdzierzanowski, 2015/03/05 21:00:05]

Done.

 
-template <>
-struct TrampolineHelper<void()> {
+template <typename... Args>
+struct TrampolineHelper<void(Args...)> {
   static void Run(
       const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-      const base::Callback<void()>& cb) {
-    task_runner->PostTask(FROM_HERE, base::Bind(cb));
+      const base::Callback<void(Args...)>& cb,
+      Args... args) {
+    task_runner->PostTask(FROM_HERE,
+                          base::Bind(cb, internal::TrampolineForward(args)...));

[xhwang, 2015/03/05 17:19:15]

internal not needed?

[wdzierzanowski, 2015/03/05 20:45:16]

Of course not, blindly copied from the old version :)

[wdzierzanowski, 2015/03/05 20:45:16]

Of course not, blindly copied from the old version :)

[wdzierzanowski, 2015/03/05 20:47:56]

Done.

   }
 };
 
-
-template <typename A1>
-struct TrampolineHelper<void(A1)> {
-  static void Run(
-      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-      const base::Callback<void(A1)>& cb, A1 a1) {
-    task_runner->PostTask(FROM_HERE, base::Bind(cb,
-        internal::TrampolineForward(a1)));
-  }
-};
-
-
-template <typename A1, typename A2>
-struct TrampolineHelper<void(A1, A2)> {
-  static void Run(
-      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-      const base::Callback<void(A1, A2)>& cb, A1 a1, A2 a2) {
-    task_runner->PostTask(FROM_HERE, base::Bind(cb,
-        internal::TrampolineForward(a1), internal::TrampolineForward(a2)));
-  }
-};
-
-
-template <typename A1, typename A2, typename A3>
-struct TrampolineHelper<void(A1, A2, A3)> {
-  static void Run(
-      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-      const base::Callback<void(A1, A2, A3)>& cb, A1 a1, A2 a2, A3 a3) {
-    task_runner->PostTask(FROM_HERE, base::Bind(cb,
-        internal::TrampolineForward(a1), internal::TrampolineForward(a2),
-        internal::TrampolineForward(a3)));
-  }
-};
-
-
-template <typename A1, typename A2, typename A3, typename A4>
-struct TrampolineHelper<void(A1, A2, A3, A4)> {
-  static void Run(
-      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-      const base::Callback<void(A1, A2, A3, A4)>& cb, A1 a1, A2 a2, A3 a3,
-          A4 a4) {
-    task_runner->PostTask(FROM_HERE, base::Bind(cb,
-        internal::TrampolineForward(a1), internal::TrampolineForward(a2),
-        internal::TrampolineForward(a3), internal::TrampolineForward(a4)));
-  }
-};
-
-
-template <typename A1, typename A2, typename A3, typename A4, typename A5>
-struct TrampolineHelper<void(A1, A2, A3, A4, A5)> {
-  static void Run(
-      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-      const base::Callback<void(A1, A2, A3, A4, A5)>& cb, A1 a1, A2 a2, A3 a3,
-          A4 a4, A5 a5) {
-    task_runner->PostTask(FROM_HERE, base::Bind(cb,
-        internal::TrampolineForward(a1), internal::TrampolineForward(a2),
-        internal::TrampolineForward(a3), internal::TrampolineForward(a4),
-        internal::TrampolineForward(a5)));
-  }
-};
-
-
-template <typename A1, typename A2, typename A3, typename A4, typename A5,
-    typename A6>
-struct TrampolineHelper<void(A1, A2, A3, A4, A5, A6)> {
-  static void Run(
-      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-      const base::Callback<void(A1, A2, A3, A4, A5, A6)>& cb, A1 a1, A2 a2,
-          A3 a3, A4 a4, A5 a5, A6 a6) {
-    task_runner->PostTask(FROM_HERE, base::Bind(cb,
-        internal::TrampolineForward(a1), internal::TrampolineForward(a2),
-        internal::TrampolineForward(a3), internal::TrampolineForward(a4),
-        internal::TrampolineForward(a5), internal::TrampolineForward(a6)));
-  }
-};
-
-
-template <typename A1, typename A2, typename A3, typename A4, typename A5,
-    typename A6, typename A7>
-struct TrampolineHelper<void(A1, A2, A3, A4, A5, A6, A7)> {
-  static void Run(
-      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
-      const base::Callback<void(A1, A2, A3, A4, A5, A6, A7)>& cb, A1 a1, A2 a2,
-          A3 a3, A4 a4, A5 a5, A6 a6, A7 a7) {
-    task_runner->PostTask(FROM_HERE, base::Bind(cb,
-        internal::TrampolineForward(a1), internal::TrampolineForward(a2),
-        internal::TrampolineForward(a3), internal::TrampolineForward(a4),
-        internal::TrampolineForward(a5), internal::TrampolineForward(a6),
-        internal::TrampolineForward(a7)));
-  }
-};
-
-
 }  // namespace internal
 
 template<typename T>
 static base::Callback<T> BindToCurrentLoop(
     const base::Callback<T>& cb) {
   return base::Bind(&internal::TrampolineHelper<T>::Run,
                     base::MessageLoopProxy::current(), cb);
 }
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_