The Tor Browser: mfbt/TypedEnum.h@97036ab72558 (annotated)

mfbt/TypedEnum.h@97036ab72558 (annotated)

mfbt/TypedEnum.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.

 /* -*- 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/. */
 /* Macros to emulate C++11 typed enums and enum classes. */
 #ifndef mozilla_TypedEnum_h
 #define mozilla_TypedEnum_h
 #include "mozilla/TypedEnumInternal.h"
 #include "mozilla/MacroArgs.h"
 #if defined(__cplusplus)
 /**
  * MOZ_ENUM_TYPE specifies the underlying numeric type for an enum.  It's
  * specified by placing MOZ_ENUM_TYPE(type) immediately after the enum name in
  * its declaration, and before the opening curly brace, like
  *
  *   enum MyEnum MOZ_ENUM_TYPE(uint16_t)
  *   {
  *     A,
  *     B = 7,
  *     C
  *   };
  *
  * In supporting compilers, the macro will expand to ": uint16_t".  The
  * compiler will allocate exactly two bytes for MyEnum and will require all
  * enumerators to have values between 0 and 65535.  (Thus specifying "B =
  * 100000" instead of "B = 7" would fail to compile.)  In old compilers the
  * macro expands to the empty string, and the underlying type is generally
  * undefined.
  */
 #ifdef MOZ_HAVE_CXX11_ENUM_TYPE
 #  define MOZ_ENUM_TYPE(type)   : type
 #else
 #  define MOZ_ENUM_TYPE(type)   /* no support */
 #endif
 /**
  * MOZ_BEGIN_ENUM_CLASS and MOZ_END_ENUM_CLASS provide access to the
  * strongly-typed enumeration feature of C++11 ("enum class").  If supported
  * by the compiler, an enum defined using these macros will not be implicitly
  * converted to any other type, and its enumerators will be scoped using the
  * enumeration name.  Place MOZ_BEGIN_ENUM_CLASS(EnumName [, type]) in place of
  * "enum EnumName {", and MOZ_END_ENUM_CLASS(EnumName) in place of the closing
  * "};".  For example,
  *
  *   MOZ_BEGIN_ENUM_CLASS(Enum, int32_t)
  *     A,
  *     B = 6
  *   MOZ_END_ENUM_CLASS(Enum)
  *
  * This will make "Enum::A" and "Enum::B" appear in the global scope, but "A"
  * and "B" will not.  In compilers that support C++11 strongly-typed
  * enumerations, implicit conversions of Enum values to numeric types will
  * fail.  In other compilers, Enum itself will actually be defined as a class,
  * and some implicit conversions will fail while others will succeed.
  *
  * The optional type argument specifies the underlying type for the enum where
  * supported, as with MOZ_ENUM_TYPE().  As with MOZ_ENUM_TYPE(), it will do
  * nothing on compilers that do not support it.
  *
  * MOZ_{BEGIN,END}_ENUM_CLASS doesn't work for defining enum classes nested
  * inside classes.  To define an enum class nested inside another class, use
  * MOZ_{BEGIN,END}_NESTED_ENUM_CLASS, and place a MOZ_FINISH_NESTED_ENUM_CLASS
  * in namespace scope to handle bits that can only be implemented with
  * namespace-scoped code.  For example:
  *
  *   class FooBar {
  *
  *     MOZ_BEGIN_NESTED_ENUM_CLASS(Enum, int32_t)
  *       A,
  *       B = 6
  *     MOZ_END_NESTED_ENUM_CLASS(Enum)
  *
  *   };
  *
  *   MOZ_FINISH_NESTED_ENUM_CLASS(FooBar::Enum)
  */
 #if defined(MOZ_HAVE_CXX11_STRONG_ENUMS)
   /*
    * All compilers that support strong enums also support an explicit
    * underlying type, so no extra check is needed.
    */
    /* Single-argument form. */
 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER1(Name) \
      enum class Name {
    /* Two-argument form. */
 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER2(Name, type) \
      enum class Name : type {
 #  define MOZ_END_NESTED_ENUM_CLASS(Name) \
      };
 #  define MOZ_FINISH_NESTED_ENUM_CLASS(Name) /* nothing */
   /*
    * MOZ_ENUM_CLASS_ENUM_TYPE allows using enum classes
    * as template parameter types. For that, we need integer types.
    * In the present case where the compiler supports strong enums,
    * these are already integer types so there is nothing more to do.
    */
 #  define MOZ_ENUM_CLASS_ENUM_TYPE(Name) Name
   /*
    * See the comment below about MOZ_TEMPLATE_ENUM_CLASS_ENUM_TYPE.
    */
 #  define MOZ_TEMPLATE_ENUM_CLASS_ENUM_TYPE(Name) Name
 #else
    /**
     * We need Name to both name a type, and scope the provided enumerator
     * names.  Namespaces and classes both provide scoping, but namespaces
     * aren't types, so we need to use a class that wraps the enum values.  We
     * have an implicit conversion from the inner enum type to the class, so
     * statements like
     *
     *   Enum x = Enum::A;
     *
     * will still work.  We need to define an implicit conversion from the class
     * to the inner enum as well, so that (for instance) switch statements will
     * work.  This means that the class can be implicitly converted to a numeric
     * value as well via the enum type, since C++ allows an implicit
     * user-defined conversion followed by a standard conversion to still be
     * implicit.
     *
     * We have an explicit constructor from int defined, so that casts like
     * (Enum)7 will still work.  We also have a zero-argument constructor with
     * no arguments, so declaration without initialization (like "Enum foo;")
     * will work.
     *
     * Additionally, we'll delete as many operators as possible for the inner
     * enum type, so statements like this will still fail:
     *
     *   f(5 + Enum::B); // deleted operator+
     *
     * But we can't prevent things like this, because C++ doesn't allow
     * overriding conversions or assignment operators for enums:
     *
     *   int x = Enum::A;
     *   int f()
     *   {
     *     return Enum::A;
     *   }
     */
    /* Single-argument form. */
 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER1(Name) \
      class Name \
      { \
        public: \
          enum Enum \
          {
    /* Two-argument form. */
 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER2(Name, type) \
      class Name \
      { \
        public: \
          enum Enum MOZ_ENUM_TYPE(type) \
          {
 #  define MOZ_END_NESTED_ENUM_CLASS(Name) \
          }; \
          Name() {} \
          MOZ_CONSTEXPR Name(Enum aEnum) : mEnum(aEnum) {} \
          template<typename Other> \
          explicit MOZ_CONSTEXPR Name(Other num) : mEnum((Enum)num) {} \
          MOZ_CONSTEXPR operator Enum() const { return mEnum; } \
          explicit MOZ_CONSTEXPR Name(const mozilla::CastableTypedEnumResult<Name>& aOther) \
            : mEnum(aOther.get()) \
          {} \
        private: \
          Enum mEnum; \
      };
 #  define MOZ_FINISH_NESTED_ENUM_CLASS(Name) \
      inline int operator+(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator+(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator-(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator-(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator*(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator*(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator/(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator/(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator%(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator%(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator+(const Name::Enum&) MOZ_DELETE; \
      inline int operator-(const Name::Enum&) MOZ_DELETE; \
      inline int& operator++(Name::Enum&) MOZ_DELETE; \
      inline int operator++(Name::Enum&, int) MOZ_DELETE; \
      inline int& operator--(Name::Enum&) MOZ_DELETE; \
      inline int operator--(Name::Enum&, int) MOZ_DELETE; \
      inline bool operator==(const int&, const Name::Enum&) MOZ_DELETE; \
      inline bool operator==(const Name::Enum&, const int&) MOZ_DELETE; \
      inline bool operator!=(const int&, const Name::Enum&) MOZ_DELETE; \
      inline bool operator!=(const Name::Enum&, const int&) MOZ_DELETE; \
      inline bool operator>(const int&, const Name::Enum&) MOZ_DELETE; \
      inline bool operator>(const Name::Enum&, const int&) MOZ_DELETE; \
      inline bool operator<(const int&, const Name::Enum&) MOZ_DELETE; \
      inline bool operator<(const Name::Enum&, const int&) MOZ_DELETE; \
      inline bool operator>=(const int&, const Name::Enum&) MOZ_DELETE; \
      inline bool operator>=(const Name::Enum&, const int&) MOZ_DELETE; \
      inline bool operator<=(const int&, const Name::Enum&) MOZ_DELETE; \
      inline bool operator<=(const Name::Enum&, const int&) MOZ_DELETE; \
      inline bool operator!(const Name::Enum&) MOZ_DELETE; \
      inline bool operator&&(const bool&, const Name::Enum&) MOZ_DELETE; \
      inline bool operator&&(const Name::Enum&, const bool&) MOZ_DELETE; \
      inline bool operator||(const bool&, const Name::Enum&) MOZ_DELETE; \
      inline bool operator||(const Name::Enum&, const bool&) MOZ_DELETE; \
      inline int operator&(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator&(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator|(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator|(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator^(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator^(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator<<(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator<<(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int operator>>(const int&, const Name::Enum&) MOZ_DELETE; \
      inline int operator>>(const Name::Enum&, const int&) MOZ_DELETE; \
      inline int& operator+=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator-=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator*=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator/=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator%=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator&=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator|=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator^=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator<<=(int&, const Name::Enum&) MOZ_DELETE; \
      inline int& operator>>=(int&, const Name::Enum&) MOZ_DELETE;
   /*
    * MOZ_ENUM_CLASS_ENUM_TYPE allows using enum classes
    * as template parameter types. For that, we need integer types.
    * In the present case, the integer type is the Enum nested type.
    */
 #  define MOZ_ENUM_CLASS_ENUM_TYPE(Name) Name::Enum
   /*
    * MOZ_TEMPLATE_ENUM_CLASS_ENUM_TYPE is a variant of MOZ_ENUM_CLASS_ENUM_TYPE
    * to be used when the enum class at hand depends on template parameters.
    *
    * Indeed, if T depends on template parameters, in order to name a nested type
    * in T, C++ does not allow to just write "T::NestedType". Instead, we have
    * to write "typename T::NestedType". The role of this macro is to add
    * this "typename" keywords where needed.
    *
    * Example:
    *
    *    template<typename T, MOZ_TEMPLATE_ENUM_CLASS_ENUM_TYPE(T) Value>
    *    struct S {};
    *
    *    MOZ_BEGIN_ENUM_CLASS(E)
    *      Foo,
    *      Bar
    *    MOZ_END_ENUM_CLASS(E)
    *
    *    S<E, E::Bar> s;
    *
    * In this example, the second template parameter to S is meant to be of type T,
    * but on non-C++11 compilers, type T is a class type, not an integer type, so
    * it is not accepted as the type of a constant template parameter. One would
    * then want to use MOZ_ENUM_CLASS_ENUM_TYPE(T), but that doesn't work either
    * as T depends on template parameters (more specifically here, T _is_ a template
    * parameter) so as MOZ_ENUM_CLASS_ENUM_TYPE(T) expands to T::Enum, we are missing
    * the required "typename" keyword. So here, MOZ_TEMPLATE_ENUM_CLASS_ENUM_TYPE
    * is needed.
    */
 #  define MOZ_TEMPLATE_ENUM_CLASS_ENUM_TYPE(Name) typename Name::Enum
 #endif
 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_GLUE(a, b) a b
 #  define MOZ_BEGIN_NESTED_ENUM_CLASS(...) \
      MOZ_BEGIN_NESTED_ENUM_CLASS_GLUE( \
        MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER, \
                                       __VA_ARGS__), \
        (__VA_ARGS__))
 #  define MOZ_BEGIN_ENUM_CLASS(...) MOZ_BEGIN_NESTED_ENUM_CLASS(__VA_ARGS__)
 #  define MOZ_END_ENUM_CLASS(Name) \
      MOZ_END_NESTED_ENUM_CLASS(Name) \
      MOZ_FINISH_NESTED_ENUM_CLASS(Name)
 #endif /* __cplusplus */
 #endif /* mozilla_TypedEnum_h */

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mfbt/TypedEnum.h@97036ab72558 (annotated)

mfbt/TypedEnum.h