The Tor Browser: comparison mfbt/TypedEnum.h

--1:000000000000
+:2cce6f4e37bb
+/* -*- 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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comparison: mfbt/TypedEnum.h

mfbt/TypedEnum.h