Mojo C++ bindings: change the first template parameter of StructTraits and UnionTraits.

mojo/public/cpp/bindings/struct_traits.h

Index: mojo/public/cpp/bindings/struct_traits.h
diff --git a/mojo/public/cpp/bindings/struct_traits.h b/mojo/public/cpp/bindings/struct_traits.h
index b2a60c7887b9280d2772266bca0c3c25822e4497..c3ea5ad3dce5cd045dadadfb01caff28574170bb 100644
--- a/mojo/public/cpp/bindings/struct_traits.h
+++ b/mojo/public/cpp/bindings/struct_traits.h
@@ -8,7 +8,11 @@
 namespace mojo {
 
 // This must be specialized for any type |T| to be serialized/deserialized as
-// a mojom struct of type |MojomType|.
+// a mojom struct. |DataViewType| is the corresponding data view type of the
+// mojom struct. For example, if the mojom struct is example.Foo,
+// |DataViewType| will be example::FooDataView, which can also be referred to by
+// example::Foo::DataView (in chromium) and example::blink::Foo::DataView (in
+// blink).
 //
 // Each specialization needs to implement a few things:
 //   1. Static getters for each field in the Mojom type. These should be
@@ -20,19 +24,22 @@ namespace mojo {
 //      from |input|.
 //
 //      Serializable form of a field:
-//        Value or reference of the same type used in |MojomType|, or the
-//        following alternatives:
+//        Value or reference of the same type used in the generated stuct
+//        wrapper type, or the following alternatives:
 //        - string:
 //          Value or reference of any type that has a StringTraits defined.
-//          Supported by default: base::StringPiece, std::string.
+//          Supported by default: base::StringPiece, std::string, mojo::String,
+//          WTF::String (in blink).
 //
 //        - array:
 //          Value or reference of any type that has an ArrayTraits defined.
-//          Supported by default: std::vector, WTF::Vector (in blink), CArray.
+//          Supported by default: std::vector, CArray, mojo::Array, WTF::Vector
+//          (in blink), mojo::WTFArray (in blink).
 //
 //        - map:
 //          Value or reference of any type that has a MapTraits defined.
-//          Supported by default: std::map.
+//          Supported by default: std::map, std::unordered_map, mojo::Map,
+//          WTF::HashMap (in blink), mojo::WTFMap (in blink).
 //
 //        - struct:
 //          Value or reference of any type that has a StructTraits defined.
@@ -40,6 +47,10 @@ namespace mojo {
 //        - enum:
 //          Value of any type that has an EnumTraits defined.
 //
+//      For any nullable string/struct/array/map/union field you could also
+//      return value or reference of base::Optional<T>/WTF::Optional<T>, if T
+//      has the right *Traits defined.
+//
 //      During serialization, getters for string/struct/array/map/union fields
 //      are called twice (one for size calculation and one for actual
 //      serialization). If you want to return a value (as opposed to a
@@ -49,14 +60,13 @@ namespace mojo {
 //      Getters for fields of other types are called once.
 //
 //   2. A static Read() method to set the contents of a |T| instance from a
-//      |MojomType|DataView (e.g., if |MojomType| is test::Example, the data
-//      view will be test::ExampleDataView).
+//      DataViewType.
 //
-//        static bool Read(|MojomType|DataView data, T* output);
+//        static bool Read(DataViewType data, T* output);
 //
-//      The generated |MojomType|DataView type provides a convenient,
-//      inexpensive view of a serialized struct's field data. The caller
-//      guarantees that |!data.is_null()|.
+//      The generated DataViewType provides a convenient, inexpensive view of a
+//      serialized struct's field data. The caller guarantees that
+//      |!data.is_null()|.
 //
 //      Returning false indicates invalid incoming data and causes the message
 //      pipe receiving it to be disconnected. Therefore, you can do custom
@@ -112,9 +122,12 @@ namespace mojo {
 // reference/value to the Mojo bindings for serialization:
 //    - if T is used in the "type_mappings" section of a typemap config file,
 //      you need to declare it as pass-by-value:
-//        type_mappings = [ "MojomType=T(pass_by_value)" ]
-//    - if another type U's StructTraits has a getter for T, it needs to return
-//      non-const reference/value.
+//        type_mappings = [ "MojomType=T(move_only)" ]
+//      or
+//        type_mappings = [ "MojomType=T(copyable_pass_by_value)" ]
+//
+//    - if another type U's StructTraits/UnionTraits has a getter for T, it
+//      needs to return non-const reference/value.
 //
 // EXAMPLE:
 //
@@ -129,7 +142,7 @@ namespace mojo {
 //
 // StructTraits for Foo:
 //   template <>
-//   struct StructTraits<Foo, CustomFoo> {
+//   struct StructTraits<FooDataView, CustomFoo> {
 //     // Optional methods dealing with null:
 //     static bool IsNull(const CustomFoo& input);
 //     static void SetToNull(CustomFoo* output);
@@ -145,7 +158,7 @@ namespace mojo {
 //     static bool Read(FooDataView data, CustomFoo* output);
 //   };
 //
-template <typename MojomType, typename T>
+template <typename DataViewType, typename T>
 struct StructTraits;
 
 }  // namespace mojo