widget/windows/CheckInvariantWrapper.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 // A wrapper that uses RAII to ensure that a class invariant is checked
   8 // before and after any public function is called
   9
  10 #ifndef CHECKINVARIANTWRAPPER_H_
  11 #define CHECKINVARIANTWRAPPER_H_
  12
  13 #include "mozilla/Attributes.h"
  14 #include <utility>
  15
  16 namespace mozilla {
  17
  18 //
  19 // Wraps an object of type T and allows access to its public API by
  20 // deferencing it using the pointer syntax "->".
  21 //
  22 // Using that operator will return a temporary RAII object that
  23 // calls a method named "CheckInvariant" in its constructor, calls the
  24 // requested method, and then calls "CheckInvariant" again in its
  25 // destructor.
  26 //
  27 // The only thing your class requires is a method with the following signature:
  28 //
  29 // void CheckInvariant() const;
  30 //
  31 template <typename T>
  32 class CheckInvariantWrapper {
  33  public:
  34   class Wrapper {
  35    public:
  36     explicit Wrapper(T& aObject) : mObject(aObject) {
  37       mObject.CheckInvariant();
  38     }
  39     ~Wrapper() { mObject.CheckInvariant(); }
  40
  41     T* operator->() { return &mObject; }
  42
  43    private:
  44     T& mObject;
  45   };
  46
  47   class ConstWrapper {
  48    public:
  49     explicit ConstWrapper(const T& aObject) : mObject(aObject) {
  50       mObject.CheckInvariant();
  51     }
  52     ~ConstWrapper() { mObject.CheckInvariant(); }
  53
  54     const T* operator->() const { return &mObject; }
  55
  56    private:
  57     const T& mObject;
  58   };
  59
  60   CheckInvariantWrapper() = default;
  61
  62   MOZ_IMPLICIT CheckInvariantWrapper(T aObject) : mObject(std::move(aObject)) {}
  63
  64   template <typename... Args>
  65   explicit CheckInvariantWrapper(std::in_place_t, Args&&... args)
  66       : mObject(std::forward<Args>(args)...) {}
  67
  68   const ConstWrapper operator->() const { return ConstWrapper(mObject); }
  69
  70   Wrapper operator->() { return Wrapper(mObject); }
  71
  72  private:
  73   T mObject;
  74 };
  75
  76 }  // namespace mozilla
  77
  78 #endif  // CHECKINVARIANTWRAPPER_H_