C++ bindings

mojo/public/bindings/lib/bindings.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.
+
+#ifndef MOJO_PUBLIC_BINDINGS_LIB_BINDINGS_H_
+#define MOJO_PUBLIC_BINDINGS_LIB_BINDINGS_H_
+

[DaveMoore, 2013/10/09 17:14:11]

I find the naming of this header confusing, at least as it stands now.

To an external consumer it defines one public type, mojo::Array<T>, but it's
called "bindings.h".

For an internal consumer it defines all the rest of the types.

I think those internal types should at a minimum be broken out into their own
header that clearly indicates that they're for internal consumption only, and
have a public header that's specific to Array<T>. But we already have
bindings_internal.h. That seems odd to me.

In general there's an awful lot of magic here and I'm concerned that public
consumers of the real apis are going to have to understand a lot of it.

+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <new>
+
+#include "mojo/public/bindings/lib/buffer.h"
+#include "mojo/public/system/core.h"
+
+namespace mojo {
+
+//-----------------------------------------------------------------------------
+
+template <typename T> class Array;
+
+// UTF-8 encoded
+typedef Array<char> String;
+
+namespace internal {
+
+struct StructHeader {
+  uint32_t num_bytes;
+  uint32_t num_fields;
+};
+
+struct ArrayHeader {
+  uint32_t num_bytes;
+  uint32_t num_elements;
+};
+
+template <typename T>
+union StructPointer {
+  uint64_t offset;
+  T* ptr;
+};
+
+template <typename T>
+union ArrayPointer {
+  uint64_t offset;
+  Array<T>* ptr;
+};
+
+union StringPointer {
+  uint64_t offset;
+  String* ptr;
+};
+
+template <typename T>
+struct ArrayTraits {
+  typedef T StorageType;
+
+  static T& ToRef(StorageType& e) { return e; }
+  static T const& ToConstRef(const StorageType& e) { return e; }
+};
+
+template <typename P>
+struct ArrayTraits<P*> {
+  typedef StructPointer<P> StorageType;
+
+  static P*& ToRef(StorageType& e) { return e.ptr; }
+  static P* const& ToConstRef(const StorageType& e) { return e.ptr; }
+};
+
+template <typename T> class ObjectTraits {};
+
+}  // namespace internal
+
+//-----------------------------------------------------------------------------
+
+template <typename T>
+class Array {
+ public:
+  static Array<T>* New(Buffer* buf, size_t num_elements) {
+    size_t num_bytes = sizeof(Array<T>) + sizeof(StorageType) * num_elements;
+    return new (buf->Allocate(num_bytes)) Array<T>(num_bytes, num_elements);
+  }
+
+  template <typename U>
+  static Array<T>* NewCopyOf(Buffer* buf, const U& u) {
+    Array<T>* result = Array<T>::New(buf, u.size());
+    memcpy(result->storage(), u.data(), u.size() * sizeof(T));
+    return result;
+  }
+
+  size_t size() const { return header_.num_elements; }
+
+  T& at(size_t offset) {
+    return internal::ArrayTraits<T>::ToRef(storage()[offset]);
+  }
+
+  const T& at(size_t offset) const {
+    return internal::ArrayTraits<T>::ToConstRef(storage()[offset]);
+  }
+
+  T& operator[](size_t offset) {
+    return at(offset);
+  }
+
+  const T& operator[](size_t offset) const {
+    return at(offset);
+  }
+
+  template <typename U>
+  U To() const {
+    return U(storage(), storage() + size());
+  }
+
+ private:
+  friend class internal::ObjectTraits<Array<T> >;
+
+  typedef typename internal::ArrayTraits<T>::StorageType StorageType;
+
+  StorageType* storage() {
+    return reinterpret_cast<StorageType*>(this + 1);
+  }
+  const StorageType* storage() const {
+    return reinterpret_cast<const StorageType*>(this + 1);
+  }
+
+  Array(size_t num_bytes, size_t num_elements) {
+    header_.num_bytes = static_cast<uint32_t>(num_bytes);
+    header_.num_elements = static_cast<uint32_t>(num_elements);
+  }
+  ~Array() {}
+
+  internal::ArrayHeader header_;
+
+  // Elements of type internal::ArrayTraits<T>::StorageType follow.
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_BINDINGS_LIB_BINDINGS_H_