Mojo: more idiomatic C++ bindings

mojo/public/cpp/bindings/struct_ptr.h

+// Copyright 2014 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_STRUCT_PTR_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_
+
+#include <assert.h>
+#include <stdlib.h>
+
+#include <new>
+
+#include "mojo/public/cpp/system/macros.h"
+
+namespace mojo {
+namespace internal {
+
+template <typename Struct>
+class StructHelper {
+ public:
+  template <typename Ptr>
+  static void Initialize(Ptr* ptr) { ptr->Initialize(); }
+};
+
+}  // namespace internal
+
+template <typename Struct>
+class StructPtr {
+  MOJO_MOVE_ONLY_TYPE_FOR_CPP_03(StructPtr, RValue);
+ public:
+  StructPtr() : ptr_(NULL) {}
+  ~StructPtr() {
+    delete ptr_;
+  }
+
+  StructPtr(RValue other) : ptr_(NULL) { Take(other.object); }
+  StructPtr& operator=(RValue other) {
+    Take(other.object);
+    return *this;
+  }
+
+  template <typename U>
+  U To() const {
+    return TypeConverter<StructPtr, U>::ConvertTo(*this);
+  }
+
+  void reset() {
+    if (ptr_) {
+      delete ptr_;
+      ptr_ = NULL;
+    }
+  }
+
+  bool is_null() const { return ptr_ == NULL; }
+
+  Struct& operator*() const {
+    assert(ptr_);
+    return *ptr_;
+  }
+  Struct* operator->() const {
+    assert(ptr_);
+    return ptr_;
+  }
+  Struct* get() const { return ptr_; }
+
+  void Swap(StructPtr* other) {
+    std::swap(ptr_, other->ptr_);
+  }
+
+ private:
+  typedef Struct* StructPtr::*Testable;
+
+ public:
+  operator Testable() const { return ptr_ ? &StructPtr::ptr_ : 0; }
+
+ private:
+  friend class internal::StructHelper<Struct>;
+  void Initialize() { assert(!ptr_); ptr_ = new Struct(); }
+
+  void Take(StructPtr* other) {
+    reset();
+    Swap(other);
+  }
+
+  Struct* ptr_;
+};
+
+template <typename Struct>
+class InlinedStructPtr {
+  MOJO_MOVE_ONLY_TYPE_FOR_CPP_03(InlinedStructPtr, RValue);
+ public:
+  InlinedStructPtr() : is_null_(true) {}
+  ~InlinedStructPtr() {}
+
+  InlinedStructPtr(RValue other) : is_null_(true) { Take(other.object); }
+  InlinedStructPtr& operator=(RValue other) {
+    Take(other.object);
+    return *this;
+  }
+
+  template <typename U>
+  U To() const {
+    return TypeConverter<InlinedStructPtr, U>::ConvertTo(*this);
+  }
+
+  void reset() {
+    is_null_ = true;
+    value_.~Struct();
+    new (&value_) Struct();
+  }
+
+  bool is_null() const { return is_null_; }
+
+  Struct& operator*() const {
+    assert(!is_null_);
+    return value_;
+  }
+  Struct* operator->() const {
+    assert(!is_null_);
+    return &value_;
+  }
+  Struct* get() const { return &value_; }
+
+  void Swap(InlinedStructPtr* other) {
+    char buf[sizeof(Struct)];
+    memcpy(buf, &value_, sizeof(value_));
+    memcpy(&value_, &other->value_, sizeof(value_));
+    memcpy(&other->value_, buf, sizeof(value_));
+    std::swap(is_null_, other->is_null_);
+  }
+
+ private:
+  typedef Struct InlinedStructPtr::*Testable;
+
+ public:
+  operator Testable() const { return is_null_ ? 0 : &InlinedStructPtr::value_; }
+
+ private:
+  friend class internal::StructHelper<Struct>;
+  void Initialize() { is_null_ = false; }
+
+  void Take(InlinedStructPtr* other) {
+    reset();
+    Swap(other);
+  }
+
+  mutable Struct value_;
+  bool is_null_;
+};
+
+#if 0
+template <typename Struct, bool use_heap = (sizeof(Struct) > 28)>
+struct SelectStructPtr;
+
+template <typename Struct>
+struct SelectStructPtr<Struct, true> {
+  typedef StructPtr<Struct> type;
+};
+
+template <typename Struct>
+struct SelectStructPtr<Struct, false> {
+  typedef InlinedStructPtr<Struct> type;
+};
+#endif
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_