mfbt/DebugOnly.h@97036ab72558
mfbt/DebugOnly.h
Tue, 06 Jan 2015 21:39:09 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Tue, 06 Jan 2015 21:39:09 +0100
- branch
- TOR_BUG_9701
- changeset 8
- 97036ab72558
- permissions
- -rw-r--r--
Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.
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/. */
7 /*
8 * Provides DebugOnly, a type for variables used only in debug builds (i.e. by
9 * assertions).
10 */
12 #ifndef mozilla_DebugOnly_h
13 #define mozilla_DebugOnly_h
15 namespace mozilla {
17 /**
18 * DebugOnly contains a value of type T, but only in debug builds. In release
19 * builds, it does not contain a value. This helper is intended to be used with
20 * MOZ_ASSERT()-style macros, allowing one to write:
21 *
22 * DebugOnly<bool> check = func();
23 * MOZ_ASSERT(check);
24 *
25 * more concisely than declaring |check| conditional on #ifdef DEBUG, but also
26 * without allocating storage space for |check| in release builds.
27 *
28 * DebugOnly instances can only be coerced to T in debug builds. In release
29 * builds they don't have a value, so type coercion is not well defined.
30 *
31 * Note that DebugOnly instances still take up one byte of space, plus padding,
32 * when used as members of structs.
33 */
34 template<typename T>
35 class DebugOnly
36 {
37 public:
38 #ifdef DEBUG
39 T value;
41 DebugOnly() { }
42 DebugOnly(const T& other) : value(other) { }
43 DebugOnly(const DebugOnly& other) : value(other.value) { }
44 DebugOnly& operator=(const T& rhs) {
45 value = rhs;
46 return *this;
47 }
48 void operator++(int) {
49 value++;
50 }
51 void operator--(int) {
52 value--;
53 }
55 T* operator&() { return &value; }
57 operator T&() { return value; }
58 operator const T&() const { return value; }
60 T& operator->() { return value; }
61 const T& operator->() const { return value; }
63 #else
64 DebugOnly() { }
65 DebugOnly(const T&) { }
66 DebugOnly(const DebugOnly&) { }
67 DebugOnly& operator=(const T&) { return *this; }
68 void operator++(int) { }
69 void operator--(int) { }
70 #endif
72 /*
73 * DebugOnly must always have a destructor or else it will
74 * generate "unused variable" warnings, exactly what it's intended
75 * to avoid!
76 */
77 ~DebugOnly() {}
78 };
80 }
82 #endif /* mozilla_DebugOnly_h */
