layout/style/RustCell.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* an object with the same layout as a Rust std::cell::Cell<T> */
   8
   9 #ifndef mozilla_RustCell_h
  10 #define mozilla_RustCell_h
  11
  12 namespace mozilla {
  13
  14 /**
  15  * Object with the same layout as std::cell::Cell<T>.
  16  *
  17  * ServoBindings.toml defines a mapping so that generated bindings use a
  18  * real std::cell::Cell<T>.
  19  *
  20  * Note that while the layout matches, this doesn't have the same ABI as a
  21  * std::cell::Cell<T>, so values of this type can't be passed over FFI
  22  * functions.
  23  */
  24 template <typename T>
  25 class RustCell {
  26  public:
  27   RustCell() : mValue() {}
  28   explicit RustCell(T aValue) : mValue(aValue) {}
  29
  30   T Get() const { return mValue; }
  31   void Set(T aValue) { mValue = aValue; }
  32
  33   // That this API doesn't mirror the API of rust's Cell because all values in
  34   // C++ effectively act like they're wrapped in Cell<...> already, so this type
  35   // only exists for FFI purposes.
  36   T* AsPtr() { return &mValue; }
  37   const T* AsPtr() const { return &mValue; }
  38
  39  private:
  40   T mValue;
  41 };
  42
  43 }  // namespace mozilla
  44
  45 #endif  // mozilla_RustCell_h