The Tor Browser: mfbt/TypedEnumInternal.h@97036ab72558

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 /* Internal stuff needed by TypedEnum.h and TypedEnumBits.h. */

     9 // NOTE: When we can assume C++11 enum class support and TypedEnum.h goes away,

    10 // we should then consider folding TypedEnumInternal.h into TypedEnumBits.h.

    12 #ifndef mozilla_TypedEnumInternal_h

    13 #define mozilla_TypedEnumInternal_h

    15 #include "mozilla/Attributes.h"

    17 #if defined(__cplusplus)

    19 #if defined(__clang__)

    20    /*

    21     * Per Clang documentation, "Note that marketing version numbers should not

    22     * be used to check for language features, as different vendors use different

    23     * numbering schemes. Instead, use the feature checking macros."

    24     */

    25 #  ifndef __has_extension

    26 #    define __has_extension __has_feature /* compatibility, for older versions of clang */

    27 #  endif

    28 #  if __has_extension(cxx_strong_enums)

    29 #    define MOZ_HAVE_CXX11_ENUM_TYPE

    30 #    define MOZ_HAVE_CXX11_STRONG_ENUMS

    31 #  endif

    32 #elif defined(__GNUC__)

    33 #  if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L

    34 #    if MOZ_GCC_VERSION_AT_LEAST(4, 6, 3)

    35 #      define MOZ_HAVE_CXX11_ENUM_TYPE

    36 #      define MOZ_HAVE_CXX11_STRONG_ENUMS

    37 #    endif

    38 #  endif

    39 #elif defined(_MSC_VER)

    40 #  if _MSC_VER >= 1400

    41 #    define MOZ_HAVE_CXX11_ENUM_TYPE

    42 #  endif

    43 #  if _MSC_VER >= 1700

    44 #    define MOZ_HAVE_CXX11_STRONG_ENUMS

    45 #  endif

    46 #endif

    48 namespace mozilla {

    50 /*

    51  * The problem that CastableTypedEnumResult aims to solve is that

    52  * typed enums are not convertible to bool, and there is no way to make them

    53  * be, yet user code wants to be able to write

    54  *

    55  *   if (myFlags & Flags::SOME_PARTICULAR_FLAG)              (1)

    56  *

    57  * There are different approaches to solving this. Most of them require

    58  * adapting user code. For example, we could implement operator! and have

    59  * the user write

    60  *

    61  *   if (!!(myFlags & Flags::SOME_PARTICULAR_FLAG))          (2)

    62  *

    63  * Or we could supply a IsNonZero() or Any() function returning whether

    64  * an enum value is nonzero, and have the user write

    65  *

    66  *   if (Any(Flags & Flags::SOME_PARTICULAR_FLAG))           (3)

    67  *

    68  * But instead, we choose to preserve the original user syntax (1) as it

    69  * is inherently more readable, and to ease porting existing code to typed

    70  * enums. We achieve this by having operator& and other binary bitwise

    71  * operators have as return type a class, CastableTypedEnumResult,

    72  * that wraps a typed enum but adds bool convertibility.

    73  */

    74 template<typename E>

    75 class CastableTypedEnumResult

    76 {

    77   private:

    78     const E mValue;

    80   public:

    81     explicit MOZ_CONSTEXPR CastableTypedEnumResult(E value)

    82       : mValue(value)

    83     {}

    85     MOZ_CONSTEXPR operator E() const { return mValue; }

    87     template<typename DestinationType>

    88     MOZ_EXPLICIT_CONVERSION MOZ_CONSTEXPR

    89     operator DestinationType() const {

    90       return DestinationType(mValue);

    91     }

    93     MOZ_CONSTEXPR bool operator !() const { return !bool(mValue); }

    95 #ifndef MOZ_HAVE_CXX11_STRONG_ENUMS

    96     // This get() method is used to implement a constructor in the

    97     // non-c++11 fallback path for MOZ_BEGIN_ENUM_CLASS, taking a

    98     // CastableTypedEnumResult. If we try to implement it using the

    99     // above conversion operator E(), then at least clang 3.3

   100     // (when forced to take the non-c++11 fallback path) compiles

   101     // this constructor to an infinite recursion. So we introduce this

   102     // get() method, that does exactly the same as the conversion operator,

   103     // to work around this.

   104     MOZ_CONSTEXPR E get() const { return mValue; }

   105 #endif

   106 };

   108 } // namespace mozilla

   110 #endif // __cplusplus

   112 #endif // mozilla_TypedEnumInternal_h

The Tor Browser / file revision

mfbt/TypedEnumInternal.h@97036ab72558

mfbt/TypedEnumInternal.h