summaryrefslogtreecommitdiff
path: root/xpcom/base/OwningNonNull.h
blob: b72a250c401b346173e6be47a7cbbf17b9aea218 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* A class for non-null strong pointers to reference-counted objects. */

#ifndef mozilla_OwningNonNull_h
#define mozilla_OwningNonNull_h

#include "nsAutoPtr.h"
#include "nsCycleCollectionNoteChild.h"

namespace mozilla {

template<class T>
class OwningNonNull
{
public:
  OwningNonNull() {}

  MOZ_IMPLICIT OwningNonNull(T& aValue)
  {
    init(&aValue);
  }

  template<class U>
  MOZ_IMPLICIT OwningNonNull(already_AddRefed<U>&& aValue)
  {
    init(aValue);
  }

  template<class U>
  MOZ_IMPLICIT OwningNonNull(const OwningNonNull<U>& aValue)
  {
    init(aValue);
  }

  // This is no worse than get() in terms of const handling.
  operator T&() const
  {
    MOZ_ASSERT(mInited);
    MOZ_ASSERT(mPtr, "OwningNonNull<T> was set to null");
    return *mPtr;
  }

  operator T*() const
  {
    MOZ_ASSERT(mInited);
    MOZ_ASSERT(mPtr, "OwningNonNull<T> was set to null");
    return mPtr;
  }

  // Conversion to bool is always true, so delete to catch errors
  explicit operator bool() const = delete;

  T*
  operator->() const
  {
    MOZ_ASSERT(mInited);
    MOZ_ASSERT(mPtr, "OwningNonNull<T> was set to null");
    return mPtr;
  }

  OwningNonNull<T>&
  operator=(T* aValue)
  {
    init(aValue);
    return *this;
  }

  OwningNonNull<T>&
  operator=(T& aValue)
  {
    init(&aValue);
    return *this;
  }

  template<class U>
  OwningNonNull<T>&
  operator=(already_AddRefed<U>&& aValue)
  {
    init(aValue);
    return *this;
  }

  template<class U>
  OwningNonNull<T>&
  operator=(const OwningNonNull<U>& aValue)
  {
    init(aValue);
    return *this;
  }

  // Don't allow assigning nullptr, it makes no sense
  void operator=(decltype(nullptr)) = delete;

  already_AddRefed<T> forget()
  {
#ifdef DEBUG
    mInited = false;
#endif
    return mPtr.forget();
  }

  template<class U>
  void
  forget(U** aOther)
  {
#ifdef DEBUG
    mInited = false;
#endif
    mPtr.forget(aOther);
  }

  // Make us work with smart pointer helpers that expect a get().
  T* get() const
  {
    MOZ_ASSERT(mInited);
    MOZ_ASSERT(mPtr);
    return mPtr;
  }

  template<typename U>
  void swap(U& aOther)
  {
    mPtr.swap(aOther);
#ifdef DEBUG
    mInited = mPtr;
#endif
  }

  // We have some consumers who want to check whether we're inited in non-debug
  // builds as well.  Luckily, we have the invariant that we're inited precisely
  // when mPtr is non-null.
  bool isInitialized() const
  {
    MOZ_ASSERT(!!mPtr == mInited, "mInited out of sync with mPtr?");
    return mPtr;
  }

protected:
  template<typename U>
  void init(U&& aValue)
  {
    mPtr = aValue;
    MOZ_ASSERT(mPtr);
#ifdef DEBUG
    mInited = true;
#endif
  }

  RefPtr<T> mPtr;
#ifdef DEBUG
  bool mInited = false;
#endif
};

template <typename T>
inline void
ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
                            OwningNonNull<T>& aField,
                            const char* aName,
                            uint32_t aFlags = 0)
{
  CycleCollectionNoteChild(aCallback, aField.get(), aName, aFlags);
}

} // namespace mozilla

// Declared in nsCOMPtr.h
template<class T> template<class U>
nsCOMPtr<T>::nsCOMPtr(const mozilla::OwningNonNull<U>& aOther)
  : nsCOMPtr(aOther.get())
{}

template<class T> template<class U>
nsCOMPtr<T>&
nsCOMPtr<T>::operator=(const mozilla::OwningNonNull<U>& aOther)
{
  return operator=(aOther.get());
}

// Declared in mozilla/RefPtr.h
template<class T> template<class U>
RefPtr<T>::RefPtr(const mozilla::OwningNonNull<U>& aOther)
  : RefPtr(aOther.get())
{}

template<class T> template<class U>
RefPtr<T>&
RefPtr<T>::operator=(const mozilla::OwningNonNull<U>& aOther)
{
  return operator=(aOther.get());
}

#endif // mozilla_OwningNonNull_h