Add a variadic version of ParamTraits, to allow for >5 IPC parameters.

ipc/ipc_message_utils.h

 // Copyright (c) 2012 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 IPC_IPC_MESSAGE_UTILS_H_
 #define IPC_IPC_MESSAGE_UTILS_H_
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
@@ skipping 706 matching lines @@
   static void Write(base::Pickle* m, const param_type& p) {}
   static bool Read(const base::Pickle* m,
                    base::PickleIterator* iter,
                    param_type* r) {
     return true;
   }
   static void Log(const param_type& p, std::string* l) {
   }
 };
 
-template <class A>
-struct ParamTraits<std::tuple<A>> {
-  typedef std::tuple<A> param_type;
+template <int I, int MAX>

[Ken Rockot(use gerrit already), 2017/06/14 17:42:26]

How about counting down instead of counting up? This should read more simply:

template <int ArgIndex>
struct TupleParamTraitsHelper {
  template <T>
  ... GetSize... {
    ParamTraitsHelper<ArgIndex - 1>::GetSize(sizer, p);
    GetParamSize(sizer, std::get<ArgIndex - 1>(p));
  }
  // ...
}

and then you simply specialize <0> to do nothing in each method.

[ossu-chromium, 2017/06/20 11:57:19]

I tried it and I think my new version reads a bit clearer, although perhaps
being slightly longer, than the pre-order recursive one. I've kept it counting
up, but aliased the helper for the next step and made the end case no-ops.

+struct ParamTraitsHelper {
+  template <typename T>

[Ken Rockot(use gerrit already), 2017/06/14 17:42:27]

Not sure there's much reason to template each method separately? i.e. why not
just have:

template <int ArgIndex, typename... TupleArgs>
strict TupleParamTraitsHelper {
  using T = std::tuple<TupleArgs...>;
  // ...
};

[ossu-chromium, 2017/06/20 11:57:19]

Right. I've just put the type as a third class template argument.

+  static void GetSize(base::PickleSizer* sizer, const T& p) {
+    GetParamSize(sizer, std::get<I>(p));
+    ParamTraitsHelper<I + 1, MAX>::GetSize(sizer, p);
+  }
+
+  template <typename T>
+  static void Write(base::Pickle* m, const T& p) {
+    WriteParam(m, std::get<I>(p));
+    ParamTraitsHelper<I + 1, MAX>::Write(m, p);
+  }
+
+  template <typename T>
+  static bool Read(const base::Pickle* m, base::PickleIterator* iter, T* r) {
+    return ReadParam(m, iter, &std::get<I>(*r)) &&
+           ParamTraitsHelper<I + 1, MAX>::Read(m, iter, r);
+  }
+
+  template <typename T>
+  static void Log(const T& p, std::string* l) {
+    LogParam(std::get<I>(p), l);
+    l->append(", ");
+    ParamTraitsHelper<I + 1, MAX>::Log(p, l);
+  }
+};
+
+template <int I>
+struct ParamTraitsHelper<I, I> {
+  template <typename T>
+  static void GetSize(base::PickleSizer* sizer, const T& p) {
+    GetParamSize(sizer, std::get<I>(p));
+  }
+
+  template <typename T>
+  static void Write(base::Pickle* m, const T& p) {
+    WriteParam(m, std::get<I>(p));
+  }
+
+  template <typename T>
+  static bool Read(const base::Pickle* m, base::PickleIterator* iter, T* r) {
+    return ReadParam(m, iter, &std::get<I>(*r));
+  }
+
+  template <typename T>
+  static void Log(const T& p, std::string* l) {
+    LogParam(std::get<I>(p), l);
+  }
+};
+
+template <class... Args>
+struct ParamTraits<std::tuple<Args...>> {
+  typedef std::tuple<Args...> param_type;
+  typedef ParamTraitsHelper<0, std::tuple_size<param_type>::value - 1> Helper;
+
   static void GetSize(base::PickleSizer* sizer, const param_type& p) {
-    GetParamSize(sizer, std::get<0>(p));
+    Helper::GetSize(sizer, p);
   }
+
   static void Write(base::Pickle* m, const param_type& p) {
-    WriteParam(m, std::get<0>(p));
+    Helper::Write(m, p);
   }
+
   static bool Read(const base::Pickle* m,
                    base::PickleIterator* iter,
                    param_type* r) {
-    return ReadParam(m, iter, &std::get<0>(*r));
+    return Helper::Read(m, iter, r);
   }
-  static void Log(const param_type& p, std::string* l) {
-    LogParam(std::get<0>(p), l);
-  }
-};
 
-template <class A, class B>
-struct ParamTraits<std::tuple<A, B>> {
-  typedef std::tuple<A, B> param_type;
-  static void GetSize(base::PickleSizer* sizer, const param_type& p) {
-    GetParamSize(sizer, std::get<0>(p));
-    GetParamSize(sizer, std::get<1>(p));
-  }
-  static void Write(base::Pickle* m, const param_type& p) {
-    WriteParam(m, std::get<0>(p));
-    WriteParam(m, std::get<1>(p));
-  }
-  static bool Read(const base::Pickle* m,
-                   base::PickleIterator* iter,
-                   param_type* r) {
-    return (ReadParam(m, iter, &std::get<0>(*r)) &&
-            ReadParam(m, iter, &std::get<1>(*r)));
-  }
-  static void Log(const param_type& p, std::string* l) {
-    LogParam(std::get<0>(p), l);
-    l->append(", ");
-    LogParam(std::get<1>(p), l);
-  }
-};
-
-template <class A, class B, class C>
-struct ParamTraits<std::tuple<A, B, C>> {
-  typedef std::tuple<A, B, C> param_type;
-  static void GetSize(base::PickleSizer* sizer, const param_type& p) {
-    GetParamSize(sizer, std::get<0>(p));
-    GetParamSize(sizer, std::get<1>(p));
-    GetParamSize(sizer, std::get<2>(p));
-  }
-  static void Write(base::Pickle* m, const param_type& p) {
-    WriteParam(m, std::get<0>(p));
-    WriteParam(m, std::get<1>(p));
-    WriteParam(m, std::get<2>(p));
-  }
-  static bool Read(const base::Pickle* m,
-                   base::PickleIterator* iter,
-                   param_type* r) {
-    return (ReadParam(m, iter, &std::get<0>(*r)) &&
-            ReadParam(m, iter, &std::get<1>(*r)) &&
-            ReadParam(m, iter, &std::get<2>(*r)));
-  }
-  static void Log(const param_type& p, std::string* l) {
-    LogParam(std::get<0>(p), l);
-    l->append(", ");
-    LogParam(std::get<1>(p), l);
-    l->append(", ");
-    LogParam(std::get<2>(p), l);
-  }
-};
-
-template <class A, class B, class C, class D>
-struct ParamTraits<std::tuple<A, B, C, D>> {
-  typedef std::tuple<A, B, C, D> param_type;
-  static void GetSize(base::PickleSizer* sizer, const param_type& p) {
-    GetParamSize(sizer, std::get<0>(p));
-    GetParamSize(sizer, std::get<1>(p));
-    GetParamSize(sizer, std::get<2>(p));
-    GetParamSize(sizer, std::get<3>(p));
-  }
-  static void Write(base::Pickle* m, const param_type& p) {
-    WriteParam(m, std::get<0>(p));
-    WriteParam(m, std::get<1>(p));
-    WriteParam(m, std::get<2>(p));
-    WriteParam(m, std::get<3>(p));
-  }
-  static bool Read(const base::Pickle* m,
-                   base::PickleIterator* iter,
-                   param_type* r) {
-    return (ReadParam(m, iter, &std::get<0>(*r)) &&
-            ReadParam(m, iter, &std::get<1>(*r)) &&
-            ReadParam(m, iter, &std::get<2>(*r)) &&
-            ReadParam(m, iter, &std::get<3>(*r)));
-  }
-  static void Log(const param_type& p, std::string* l) {
-    LogParam(std::get<0>(p), l);
-    l->append(", ");
-    LogParam(std::get<1>(p), l);
-    l->append(", ");
-    LogParam(std::get<2>(p), l);
-    l->append(", ");
-    LogParam(std::get<3>(p), l);
-  }
-};
-
-template <class A, class B, class C, class D, class E>
-struct ParamTraits<std::tuple<A, B, C, D, E>> {
-  typedef std::tuple<A, B, C, D, E> param_type;
-  static void GetSize(base::PickleSizer* sizer, const param_type& p) {
-    GetParamSize(sizer, std::get<0>(p));
-    GetParamSize(sizer, std::get<1>(p));
-    GetParamSize(sizer, std::get<2>(p));
-    GetParamSize(sizer, std::get<3>(p));
-    GetParamSize(sizer, std::get<4>(p));
-  }
-  static void Write(base::Pickle* m, const param_type& p) {
-    WriteParam(m, std::get<0>(p));
-    WriteParam(m, std::get<1>(p));
-    WriteParam(m, std::get<2>(p));
-    WriteParam(m, std::get<3>(p));
-    WriteParam(m, std::get<4>(p));
-  }
-  static bool Read(const base::Pickle* m,
-                   base::PickleIterator* iter,
-                   param_type* r) {
-    return (ReadParam(m, iter, &std::get<0>(*r)) &&
-            ReadParam(m, iter, &std::get<1>(*r)) &&
-            ReadParam(m, iter, &std::get<2>(*r)) &&
-            ReadParam(m, iter, &std::get<3>(*r)) &&
-            ReadParam(m, iter, &std::get<4>(*r)));
-  }
-  static void Log(const param_type& p, std::string* l) {
-    LogParam(std::get<0>(p), l);
-    l->append(", ");
-    LogParam(std::get<1>(p), l);
-    l->append(", ");
-    LogParam(std::get<2>(p), l);
-    l->append(", ");
-    LogParam(std::get<3>(p), l);
-    l->append(", ");
-    LogParam(std::get<4>(p), l);
-  }
+  static void Log(const param_type& p, std::string* l) { Helper::Log(p, l); }
 };
 
 template <class P, size_t stack_capacity>
 struct ParamTraits<base::StackVector<P, stack_capacity> > {
   typedef base::StackVector<P, stack_capacity> param_type;
   static void GetSize(base::PickleSizer* sizer, const param_type& p) {
     GetParamSize(sizer, static_cast<int>(p->size()));
     for (size_t i = 0; i < p->size(); i++)
       GetParamSize(sizer, p[i]);
   }
@@ skipping 316 matching lines @@
 template <class ReplyParamType>
 inline void LogReplyParamsToMessage(const ReplyParamType& reply_params,
                                     const Message* msg) {}
 
 inline void ConnectMessageAndReply(const Message* msg, Message* reply) {}
 #endif
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_MESSAGE_UTILS_H_