[gin] Use variadic templates in gin/function_template.h

gin/function_template.h

Index: gin/function_template.h
diff --git a/gin/function_template.h b/gin/function_template.h
index 7ba54b5910ef4ffcb032deba86a8490a0fba72ef..955ff53c284d416b8ffa33e2011635a342476c2c 100644
--- a/gin/function_template.h
+++ b/gin/function_template.h
@@ -1,16 +1,10 @@
-// This file was GENERATED by command:
-//     pump.py function_template.h.pump
-// DO NOT EDIT BY HAND!!!
-
-
+// Copyright 2014 The Chromium Authors. All rights reserved.

[Aaron Boodman, 2014/10/31 22:26:40]

I thought we weren't supposed to change the year.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
 
 #ifndef GIN_FUNCTION_TEMPLATE_H_
 #define GIN_FUNCTION_TEMPLATE_H_
 
-// Copyright 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.
-
 #include "base/callback.h"
 #include "base/logging.h"
 #include "gin/arguments.h"
@@ -80,180 +74,6 @@ class CallbackHolder : public CallbackHolderBase {
   DISALLOW_COPY_AND_ASSIGN(CallbackHolder);
 };
 
-
-// This set of templates invokes a base::Callback, converts the return type to a
-// JavaScript value, and returns that value to script via the provided
-// gin::Arguments object.
-//
-// In C++, you can declare the function foo(void), but you can't pass a void
-// expression to foo. As a result, we must specialize the case of Callbacks that
-// have the void return type.
-template<typename R, typename P1 = void, typename P2 = void,
-    typename P3 = void, typename P4 = void, typename P5 = void,
-    typename P6 = void>
-struct Invoker {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<R(P1, P2, P3, P4, P5, P6)>& callback,
-      const P1& a1,
-      const P2& a2,
-      const P3& a3,
-      const P4& a4,
-      const P5& a5,
-      const P6& a6) {
-    args->Return(callback.Run(a1, a2, a3, a4, a5, a6));
-  }
-};
-template<typename P1, typename P2, typename P3, typename P4, typename P5,
-    typename P6>
-struct Invoker<void, P1, P2, P3, P4, P5, P6> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<void(P1, P2, P3, P4, P5, P6)>& callback,
-      const P1& a1,
-      const P2& a2,
-      const P3& a3,
-      const P4& a4,
-      const P5& a5,
-      const P6& a6) {
-    callback.Run(a1, a2, a3, a4, a5, a6);
-  }
-};
-
-template<typename R, typename P1, typename P2, typename P3, typename P4,
-    typename P5>
-struct Invoker<R, P1, P2, P3, P4, P5, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<R(P1, P2, P3, P4, P5)>& callback,
-      const P1& a1,
-      const P2& a2,
-      const P3& a3,
-      const P4& a4,
-      const P5& a5) {
-    args->Return(callback.Run(a1, a2, a3, a4, a5));
-  }
-};
-template<typename P1, typename P2, typename P3, typename P4, typename P5>
-struct Invoker<void, P1, P2, P3, P4, P5, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<void(P1, P2, P3, P4, P5)>& callback,
-      const P1& a1,
-      const P2& a2,
-      const P3& a3,
-      const P4& a4,
-      const P5& a5) {
-    callback.Run(a1, a2, a3, a4, a5);
-  }
-};
-
-template<typename R, typename P1, typename P2, typename P3, typename P4>
-struct Invoker<R, P1, P2, P3, P4, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<R(P1, P2, P3, P4)>& callback,
-      const P1& a1,
-      const P2& a2,
-      const P3& a3,
-      const P4& a4) {
-    args->Return(callback.Run(a1, a2, a3, a4));
-  }
-};
-template<typename P1, typename P2, typename P3, typename P4>
-struct Invoker<void, P1, P2, P3, P4, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<void(P1, P2, P3, P4)>& callback,
-      const P1& a1,
-      const P2& a2,
-      const P3& a3,
-      const P4& a4) {
-    callback.Run(a1, a2, a3, a4);
-  }
-};
-
-template<typename R, typename P1, typename P2, typename P3>
-struct Invoker<R, P1, P2, P3, void, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<R(P1, P2, P3)>& callback,
-      const P1& a1,
-      const P2& a2,
-      const P3& a3) {
-    args->Return(callback.Run(a1, a2, a3));
-  }
-};
-template<typename P1, typename P2, typename P3>
-struct Invoker<void, P1, P2, P3, void, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<void(P1, P2, P3)>& callback,
-      const P1& a1,
-      const P2& a2,
-      const P3& a3) {
-    callback.Run(a1, a2, a3);
-  }
-};
-
-template<typename R, typename P1, typename P2>
-struct Invoker<R, P1, P2, void, void, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<R(P1, P2)>& callback,
-      const P1& a1,
-      const P2& a2) {
-    args->Return(callback.Run(a1, a2));
-  }
-};
-template<typename P1, typename P2>
-struct Invoker<void, P1, P2, void, void, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<void(P1, P2)>& callback,
-      const P1& a1,
-      const P2& a2) {
-    callback.Run(a1, a2);
-  }
-};
-
-template<typename R, typename P1>
-struct Invoker<R, P1, void, void, void, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<R(P1)>& callback,
-      const P1& a1) {
-    args->Return(callback.Run(a1));
-  }
-};
-template<typename P1>
-struct Invoker<void, P1, void, void, void, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<void(P1)>& callback,
-      const P1& a1) {
-    callback.Run(a1);
-  }
-};
-
-template<typename R>
-struct Invoker<R, void, void, void, void, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<R()>& callback) {
-    args->Return(callback.Run());
-  }
-};
-template<>
-struct Invoker<void, void, void, void, void, void, void> {
-  inline static void Go(
-      Arguments* args,
-      const base::Callback<void()>& callback) {
-    callback.Run();
-  }
-};
-
-
 template<typename T>
 bool GetNextArgument(Arguments* args, int create_flags, bool is_first,
                      T* result) {
@@ -284,170 +104,88 @@ inline bool GetNextArgument(Arguments* args, int create_flags,
   return true;
 }
 
+// Classes for generating and storing an argument pack of integer indices
+// (based on well-known "indices trick", see: http://goo.gl/bKKojn):
+template <size_t... indices>
+struct IndicesHolder {};
 
-// DispatchToCallback converts all the JavaScript arguments to C++ types and
-// invokes the base::Callback.
-template<typename Sig>
-struct Dispatcher {
+template <size_t requested_index, size_t... indices>
+struct IndicesGenerator {
+  using type = typename IndicesGenerator<requested_index - 1,
+                                         requested_index - 1,
+                                         indices...>::type;
 };
-
-template<typename R>
-struct Dispatcher<R()> {
-  static void DispatchToCallback(
-      const v8::FunctionCallbackInfo<v8::Value>& info) {
-    Arguments args(info);
-    v8::Handle<v8::External> v8_holder;
-    CHECK(args.GetData(&v8_holder));
-    CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
-        v8_holder->Value());
-
-    typedef CallbackHolder<R()> HolderT;
-    HolderT* holder = static_cast<HolderT*>(holder_base);
-
-    Invoker<R>::Go(&args, holder->callback);
-  }
+template <size_t... indices>
+struct IndicesGenerator<0, indices...> {
+  using type = IndicesHolder<indices...>;
 };
 
-template<typename R, typename P1>
-struct Dispatcher<R(P1)> {
-  static void DispatchToCallback(
-      const v8::FunctionCallbackInfo<v8::Value>& info) {
-    Arguments args(info);
-    v8::Handle<v8::External> v8_holder;
-    CHECK(args.GetData(&v8_holder));
-    CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
-        v8_holder->Value());
+// Class template for extracting and storing single argument for callback
+// at position |index|.
+template <size_t index, typename ArgType>
+struct ArgumentHolder {
+  using ArgLocalType = typename CallbackParamTraits<ArgType>::LocalType;
 
-    typedef CallbackHolder<R(P1)> HolderT;
-    HolderT* holder = static_cast<HolderT*>(holder_base);
-
-    typename CallbackParamTraits<P1>::LocalType a1;
-    if (!GetNextArgument(&args, holder->flags, true, &a1)) {
-      args.ThrowError();
-      return;
-    }
+  ArgLocalType value;
+  bool ok;
 
-    Invoker<R, P1>::Go(&args, holder->callback, a1);
+  ArgumentHolder(Arguments* args, int create_flags)
+      : ok(GetNextArgument(args, create_flags, index == 0, &value)) {

[Aaron Boodman, 2014/10/31 22:26:40]

Out of curiosity, since you have |index| already, if we changed gin::Arguments
to have a getter by index, could we use that and avoid the slighty scary comment
about below initialization order?

[Krzysztof Olczyk, 2014/11/05 07:50:40]

Yes, we could have probably used the index directly if gin::Arguments supported
it, but it might have complicated the code - taking into account the fact that
we do not directly iterate over gin::Arguments, as some of the arguments can be
gin::Arguments* or v8::Isolate*. 
So, we would have needed to know at which position they were and add adequate
offsets.

+    if (!ok)
+      args->ThrowError();
   }
 };
 
-template<typename R, typename P1, typename P2>
-struct Dispatcher<R(P1, P2)> {
-  static void DispatchToCallback(
-      const v8::FunctionCallbackInfo<v8::Value>& info) {
-    Arguments args(info);
-    v8::Handle<v8::External> v8_holder;
-    CHECK(args.GetData(&v8_holder));
-    CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
-        v8_holder->Value());
-
-    typedef CallbackHolder<R(P1, P2)> HolderT;
-    HolderT* holder = static_cast<HolderT*>(holder_base);
+// Class template for converting arguments from JavaScript to C++ and running
+// the callback with them.
+template <typename IndicesType, typename... ArgTypes>
+class Invoker {};
 
-    typename CallbackParamTraits<P1>::LocalType a1;
-    typename CallbackParamTraits<P2>::LocalType a2;
-    if (!GetNextArgument(&args, holder->flags, true, &a1) ||
-        !GetNextArgument(&args, holder->flags, false, &a2)) {
-      args.ThrowError();
-      return;
-    }
+template <size_t... indices, typename... ArgTypes>
+class Invoker<IndicesHolder<indices...>, ArgTypes...>
+    : public ArgumentHolder<indices, ArgTypes>... {
+ public:
+  // Invoker<> inherits from ArgumentHolder<> for each argument.
+  // C++ has always been strict about the class initialization order,
+  // so it is guaranteed ArgumentHolders will be initialized (and thus, will
+  // extract arguments from Arguments) in the right order.
+  Invoker(Arguments* args, int create_flags)
+      : ArgumentHolder<indices, ArgTypes>(args, create_flags)...,
+        args_(args) {}
 
-    Invoker<R, P1, P2>::Go(&args, holder->callback, a1, a2);
+  bool IsOK() {
+    return And(ArgumentHolder<indices, ArgTypes>::ok...);
   }
-};
-
-template<typename R, typename P1, typename P2, typename P3>
-struct Dispatcher<R(P1, P2, P3)> {
-  static void DispatchToCallback(
-      const v8::FunctionCallbackInfo<v8::Value>& info) {
-    Arguments args(info);
-    v8::Handle<v8::External> v8_holder;
-    CHECK(args.GetData(&v8_holder));
-    CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
-        v8_holder->Value());
 
-    typedef CallbackHolder<R(P1, P2, P3)> HolderT;
-    HolderT* holder = static_cast<HolderT*>(holder_base);
-
-    typename CallbackParamTraits<P1>::LocalType a1;
-    typename CallbackParamTraits<P2>::LocalType a2;
-    typename CallbackParamTraits<P3>::LocalType a3;
-    if (!GetNextArgument(&args, holder->flags, true, &a1) ||
-        !GetNextArgument(&args, holder->flags, false, &a2) ||
-        !GetNextArgument(&args, holder->flags, false, &a3)) {
-      args.ThrowError();
-      return;
-    }
-
-    Invoker<R, P1, P2, P3>::Go(&args, holder->callback, a1, a2, a3);
+  template <typename ReturnType>
+  void DispatchToCallback(base::Callback<ReturnType(ArgTypes...)> callback) {
+    args_->Return(callback.Run(ArgumentHolder<indices, ArgTypes>::value...));
   }
-};
 
-template<typename R, typename P1, typename P2, typename P3, typename P4>
-struct Dispatcher<R(P1, P2, P3, P4)> {
-  static void DispatchToCallback(
-      const v8::FunctionCallbackInfo<v8::Value>& info) {
-    Arguments args(info);
-    v8::Handle<v8::External> v8_holder;
-    CHECK(args.GetData(&v8_holder));
-    CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
-        v8_holder->Value());
-
-    typedef CallbackHolder<R(P1, P2, P3, P4)> HolderT;
-    HolderT* holder = static_cast<HolderT*>(holder_base);
-
-    typename CallbackParamTraits<P1>::LocalType a1;
-    typename CallbackParamTraits<P2>::LocalType a2;
-    typename CallbackParamTraits<P3>::LocalType a3;
-    typename CallbackParamTraits<P4>::LocalType a4;
-    if (!GetNextArgument(&args, holder->flags, true, &a1) ||
-        !GetNextArgument(&args, holder->flags, false, &a2) ||
-        !GetNextArgument(&args, holder->flags, false, &a3) ||
-        !GetNextArgument(&args, holder->flags, false, &a4)) {
-      args.ThrowError();
-      return;
-    }
-
-    Invoker<R, P1, P2, P3, P4>::Go(&args, holder->callback, a1, a2, a3, a4);
+  // In C++, you can declare the function foo(void), but you can't pass a void
+  // expression to foo. As a result, we must specialize the case of Callbacks
+  // that have the void return type.
+  void DispatchToCallback(base::Callback<void(ArgTypes...)> callback) {
+    callback.Run(ArgumentHolder<indices, ArgTypes>::value...);
   }
-};
 
-template<typename R, typename P1, typename P2, typename P3, typename P4,
-    typename P5>
-struct Dispatcher<R(P1, P2, P3, P4, P5)> {
-  static void DispatchToCallback(
-      const v8::FunctionCallbackInfo<v8::Value>& info) {
-    Arguments args(info);
-    v8::Handle<v8::External> v8_holder;
-    CHECK(args.GetData(&v8_holder));
-    CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
-        v8_holder->Value());
-
-    typedef CallbackHolder<R(P1, P2, P3, P4, P5)> HolderT;
-    HolderT* holder = static_cast<HolderT*>(holder_base);
-
-    typename CallbackParamTraits<P1>::LocalType a1;
-    typename CallbackParamTraits<P2>::LocalType a2;
-    typename CallbackParamTraits<P3>::LocalType a3;
-    typename CallbackParamTraits<P4>::LocalType a4;
-    typename CallbackParamTraits<P5>::LocalType a5;
-    if (!GetNextArgument(&args, holder->flags, true, &a1) ||
-        !GetNextArgument(&args, holder->flags, false, &a2) ||
-        !GetNextArgument(&args, holder->flags, false, &a3) ||
-        !GetNextArgument(&args, holder->flags, false, &a4) ||
-        !GetNextArgument(&args, holder->flags, false, &a5)) {
-      args.ThrowError();
-      return;
-    }
-
-    Invoker<R, P1, P2, P3, P4, P5>::Go(&args, holder->callback, a1, a2, a3, a4,
-        a5);
+ private:
+  static bool And() { return true; }
+  template <typename... T>
+  static bool And(bool arg1, T... args) {
+    return arg1 && And(args...);
   }
+
+  Arguments* args_;
 };
 
-template<typename R, typename P1, typename P2, typename P3, typename P4,
-    typename P5, typename P6>
-struct Dispatcher<R(P1, P2, P3, P4, P5, P6)> {
+// DispatchToCallback converts all the JavaScript arguments to C++ types and
+// invokes the base::Callback.
+template <typename Sig>
+struct Dispatcher {};
+
+template <typename ReturnType, typename... ArgTypes>
+struct Dispatcher<ReturnType(ArgTypes...)> {
   static void DispatchToCallback(
       const v8::FunctionCallbackInfo<v8::Value>& info) {
     Arguments args(info);
@@ -456,27 +194,13 @@ struct Dispatcher<R(P1, P2, P3, P4, P5, P6)> {
     CallbackHolderBase* holder_base = reinterpret_cast<CallbackHolderBase*>(
         v8_holder->Value());
 
-    typedef CallbackHolder<R(P1, P2, P3, P4, P5, P6)> HolderT;
+    typedef CallbackHolder<ReturnType(ArgTypes...)> HolderT;
     HolderT* holder = static_cast<HolderT*>(holder_base);
 
-    typename CallbackParamTraits<P1>::LocalType a1;
-    typename CallbackParamTraits<P2>::LocalType a2;
-    typename CallbackParamTraits<P3>::LocalType a3;
-    typename CallbackParamTraits<P4>::LocalType a4;
-    typename CallbackParamTraits<P5>::LocalType a5;
-    typename CallbackParamTraits<P6>::LocalType a6;
-    if (!GetNextArgument(&args, holder->flags, true, &a1) ||
-        !GetNextArgument(&args, holder->flags, false, &a2) ||
-        !GetNextArgument(&args, holder->flags, false, &a3) ||
-        !GetNextArgument(&args, holder->flags, false, &a4) ||
-        !GetNextArgument(&args, holder->flags, false, &a5) ||
-        !GetNextArgument(&args, holder->flags, false, &a6)) {
-      args.ThrowError();
-      return;
-    }
-
-    Invoker<R, P1, P2, P3, P4, P5, P6>::Go(&args, holder->callback, a1, a2, a3,
-        a4, a5, a6);
+    using Indices = typename IndicesGenerator<sizeof...(ArgTypes)>::type;
+    Invoker<Indices, ArgTypes...> invoker(&args, holder->flags);
+    if (invoker.IsOK())
+      invoker.DispatchToCallback(holder->callback);
   }
 };