Introducing gpu::CommandBufferId as a distinct, IdType<...>-based type.

gpu/command_buffer/common/id_type.h

Index: gpu/command_buffer/common/id_type.h
diff --git a/content/common/id_type.h b/gpu/command_buffer/common/id_type.h
similarity index 78%
rename from content/common/id_type.h
rename to gpu/command_buffer/common/id_type.h
index 5e1c45353acf3ea642b8ebba92c54509020d3511..a72daab14ee78db739c1e86f9e364ae2a87dc22c 100644
--- a/content/common/id_type.h
+++ b/gpu/command_buffer/common/id_type.h
@@ -2,14 +2,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CONTENT_COMMON_ID_TYPE_H_
-#define CONTENT_COMMON_ID_TYPE_H_
+#ifndef GPU_COMMAND_BUFFER_COMMON_ID_TYPE_H_
+#define GPU_COMMAND_BUFFER_COMMON_ID_TYPE_H_
 
 #include <stdint.h>
 #include <cstddef>
 #include <ostream>
 #include <type_traits>
 
+#include "base/pickle.h"
+#include "ipc/ipc_message_utils.h"
+#include "ipc/ipc_param_traits.h"

[piman, 2016/02/09 23:29:32]

gpu/command_buffer shouldn't depend on IPC. You can move the ParamTraits into
gpu/ipc/  (either gpu_command_buffer_traits.h or in a separate header).

[Łukasz Anforowicz, 2016/02/10 22:18:14]

Done (into a separate gpu/ipc/id_type_traits.h header).

I am a bit sad that including id_type.h won't anymore be sufficient when using
it in IPC messages - one will also have to make sure that id_type_traits.h are
included next to message definitions (unlike with traits defined in
ipc/ipc_message_utils.h which we can only do if id_type.h lives in //base or
other layer below //ipc and unlike with traits defined within id_type.h header
itself). :-(

+
 // IdType32<>, IdType64<>, etc. wrap an integer id in a custom, type-safe type.
 //
 // IdType32<Foo> is an alternative to int, for a class Foo with methods like:
@@ -28,7 +32,7 @@
 //   IdType32<T> / IdTypeU32<T>: Signed / unsigned 32-bit IDs
 //   IdType64<T> / IdTypeU64<T>: Signed / unsigned 64-bit IDs
 //   IdType<>: For when you need a different underlying type or
-//             a default/invalid value other than zero.
+//             a default/null value other than zero.
 //
 // IdType32<Foo> behaves just like an int32_t in the following aspects:
 // - it can be used as a key in std::map and/or std::unordered_map;
@@ -42,7 +46,7 @@
 // - it ensures initialization to zero and allows checking against
 //   default-initialized values via is_null method.
 
-namespace content {
+namespace gpu {
 
 template <typename TypeMarker, typename WrappedType, WrappedType kInvalidValue>
 class IdType {
@@ -102,6 +106,31 @@ std::ostream& operator<<(
   return stream << id.GetUnsafeValue();
 }
 
-}  // namespace content
+}  // namespace gpu
+
+namespace IPC {
+
+template <typename TypeMarker, typename WrappedType, WrappedType kInvalidValue>
+struct ParamTraits<gpu::IdType<TypeMarker, WrappedType, kInvalidValue>> {
+  typedef gpu::IdType<TypeMarker, WrappedType, kInvalidValue> param_type;
+  typedef ParamTraits<WrappedType> base_param_traits;
+  static void Write(base::Pickle* m, const param_type& p) {
+    base_param_traits::Write(m, p.GetUnsafeValue());
+  }
+  static bool Read(const base::Pickle* m,
+                   base::PickleIterator* iter,
+                   param_type* r) {
+    WrappedType value;
+    if (!base_param_traits::Read(m, iter, &value))
+      return false;
+    *r = param_type::FromUnsafeValue(value);
+    return true;
+  }
+  static void Log(const param_type& p, std::string* l) {
+    base_param_traits::Log(p.GetUnsafeValue(), l);
+  }
+};
+
+}  // namespace IPC
 
 #endif  // CONTENT_COMMON_ID_TYPE_H_