Add ArrayTraits<CArray<T>> utility template

mojo/public/cpp/bindings/array_traits_carray.h

+// Copyright 2016 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 MOJO_PUBLIC_CPP_BINDINGS_ARRAY_TRAITS_CARRAY_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_ARRAY_TRAITS_CARRAY_H_
+
+#include "mojo/public/cpp/bindings/array_traits.h"
+
+namespace mojo {
+
+template <typename T>
+struct CArray {
+  CArray() : size(0), max_size(0), data(nullptr) {}
+  CArray(size_t size, size_t max_size, T* data)
+      : size(size), max_size(max_size), data(data) {}
+  size_t size;
+  const size_t max_size;
+  T* const data;
+};
+
+template <typename T>
+struct ArrayTraits<CArray<T>> {
+  using Element = T;
+
+  static bool IsNull(const CArray<T>& input) { return !input.data; }

[yzshen1, 2016/06/08 16:09:17]

SetToNull() is also needed. That means we either need to make |data| an in/out;
or add another field.

+
+  static size_t GetSize(const CArray<T>& input) { return input.size; }
+
+  static T* GetData(CArray<T>& input) { return input.data; }
+
+  static const T* GetData(const CArray<T>& input) { return input.data; }
+
+  static T& GetAt(CArray<T>& input, size_t index) { return input.data[index]; }
+
+  static const T& GetAt(const CArray<T>& input, size_t index) {
+    return input.data[index];
+  }
+
+  static bool Resize(CArray<T>& input, size_t size) {
+    if (size > input.max_size)
+      return false;
+
+    input.size = size;
+    return true;
+  }
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_ARRAY_TRAITS_CARRAY_H_