mfbt/TypedEnum.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 /* Macros to emulate C++11 typed enums and enum classes. */
   7
   8 #ifndef mozilla_TypedEnum_h_
   9 #define mozilla_TypedEnum_h_
  10
  11 #include "mozilla/Attributes.h"
  12
  13 #if defined(__cplusplus)
  14
  15 #if defined(__clang__)
  16    /*
  17     * Per Clang documentation, "Note that marketing version numbers should not
  18     * be used to check for language features, as different vendors use different
  19     * numbering schemes. Instead, use the feature checking macros."
  20     */
  21 #  ifndef __has_extension
  22 #    define __has_extension __has_feature /* compatibility, for older versions of clang */
  23 #  endif
  24 #  if __has_extension(cxx_strong_enums)
  25 #    define MOZ_HAVE_CXX11_ENUM_TYPE
  26 #    define MOZ_HAVE_CXX11_STRONG_ENUMS
  27 #  endif
  28 #elif defined(__GNUC__)
  29 #  if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
  30 #    if MOZ_GCC_VERSION_AT_LEAST(4, 5, 1)
  31 #      define MOZ_HAVE_CXX11_ENUM_TYPE
  32 #      define MOZ_HAVE_CXX11_STRONG_ENUMS
  33 #    endif
  34 #  endif
  35 #elif defined(_MSC_VER)
  36 #  if _MSC_VER >= 1400
  37 #    define MOZ_HAVE_CXX11_ENUM_TYPE
  38 #  endif
  39 #  if _MSC_VER >= 1700
  40 #    define MOZ_HAVE_CXX11_STRONG_ENUMS
  41 #  endif
  42 #endif
  43
  44 /**
  45  * MOZ_ENUM_TYPE specifies the underlying numeric type for an enum.  It's
  46  * specified by placing MOZ_ENUM_TYPE(type) immediately after the enum name in
  47  * its declaration, and before the opening curly brace, like
  48  *
  49  *   enum MyEnum MOZ_ENUM_TYPE(uint16_t)
  50  *   {
  51  *     A,
  52  *     B = 7,
  53  *     C
  54  *   };
  55  *
  56  * In supporting compilers, the macro will expand to ": uint16_t".  The
  57  * compiler will allocate exactly two bytes for MyEnum and will require all
  58  * enumerators to have values between 0 and 65535.  (Thus specifying "B =
  59  * 100000" instead of "B = 7" would fail to compile.)  In old compilers the
  60  * macro expands to the empty string, and the underlying type is generally
  61  * undefined.
  62  */
  63 #ifdef MOZ_HAVE_CXX11_ENUM_TYPE
  64 #  define MOZ_ENUM_TYPE(type)   : type
  65 #else
  66 #  define MOZ_ENUM_TYPE(type)   /* no support */
  67 #endif
  68
  69 /**
  70  * MOZ_BEGIN_ENUM_CLASS and MOZ_END_ENUM_CLASS provide access to the
  71  * strongly-typed enumeration feature of C++11 ("enum class").  If supported
  72  * by the compiler, an enum defined using these macros will not be implicitly
  73  * converted to any other type, and its enumerators will be scoped using the
  74  * enumeration name.  Place MOZ_BEGIN_ENUM_CLASS(EnumName, type) in place of
  75  * "enum EnumName {", and MOZ_END_ENUM_CLASS(EnumName) in place of the closing
  76  * "};".  For example,
  77  *
  78  *   MOZ_BEGIN_ENUM_CLASS(Enum, int32_t)
  79  *     A,
  80  *     B = 6
  81  *   MOZ_END_ENUM_CLASS(Enum)
  82  *
  83  * This will make "Enum::A" and "Enum::B" appear in the global scope, but "A"
  84  * and "B" will not.  In compilers that support C++11 strongly-typed
  85  * enumerations, implicit conversions of Enum values to numeric types will
  86  * fail.  In other compilers, Enum itself will actually be defined as a class,
  87  * and some implicit conversions will fail while others will succeed.
  88  *
  89  * The type argument specifies the underlying type for the enum where
  90  * supported, as with MOZ_ENUM_TYPE().  For simplicity, it is currently
  91  * mandatory.  As with MOZ_ENUM_TYPE(), it will do nothing on compilers that do
  92  * not support it.
  93  *
  94  * Note that the workaround implemented here is not compatible with enums
  95  * nested inside a class.
  96  */
  97 #if defined(MOZ_HAVE_CXX11_STRONG_ENUMS)
  98   /*
  99    * All compilers that support strong enums also support an explicit
 100    * underlying type, so no extra check is needed.
 101    */
 102 #  define MOZ_BEGIN_ENUM_CLASS(Name, type) enum class Name : type {
 103 #  define MOZ_END_ENUM_CLASS(Name)         };
 104 #else
 105    /**
 106     * We need Name to both name a type, and scope the provided enumerator
 107     * names.  Namespaces and classes both provide scoping, but namespaces
 108     * aren't types, so we need to use a class that wraps the enum values.  We
 109     * have an implicit conversion from the inner enum type to the class, so
 110     * statements like
 111     *
 112     *   Enum x = Enum::A;
 113     *
 114     * will still work.  We need to define an implicit conversion from the class
 115     * to the inner enum as well, so that (for instance) switch statements will
 116     * work.  This means that the class can be implicitly converted to a numeric
 117     * value as well via the enum type, since C++ allows an implicit
 118     * user-defined conversion followed by a standard conversion to still be
 119     * implicit.
 120     *
 121     * We have an explicit constructor from int defined, so that casts like
 122     * (Enum)7 will still work.  We also have a zero-argument constructor with
 123     * no arguments, so declaration without initialization (like "Enum foo;")
 124     * will work.
 125     *
 126     * Additionally, we'll delete as many operators as possible for the inner
 127     * enum type, so statements like this will still fail:
 128     *
 129     *   f(5 + Enum::B); // deleted operator+
 130     *
 131     * But we can't prevent things like this, because C++ doesn't allow
 132     * overriding conversions or assignment operators for enums:
 133     *
 134     *   int x = Enum::A;
 135     *   int f()
 136     *   {
 137     *     return Enum::A;
 138     *   }
 139     */
 140 #  define MOZ_BEGIN_ENUM_CLASS(Name, type) \
 141      class Name \
 142      { \
 143        public: \
 144          enum Enum MOZ_ENUM_TYPE(type) \
 145          {
 146 #  define MOZ_END_ENUM_CLASS(Name) \
 147          }; \
 148          Name() {} \
 149          Name(Enum aEnum) : mEnum(aEnum) {} \
 150          explicit Name(int num) : mEnum((Enum)num) {} \
 151          operator Enum() const { return mEnum; } \
 152        private: \
 153          Enum mEnum; \
 154      }; \
 155      inline int operator+(const int&, const Name::Enum&) MOZ_DELETE; \
 156      inline int operator+(const Name::Enum&, const int&) MOZ_DELETE; \
 157      inline int operator-(const int&, const Name::Enum&) MOZ_DELETE; \
 158      inline int operator-(const Name::Enum&, const int&) MOZ_DELETE; \
 159      inline int operator*(const int&, const Name::Enum&) MOZ_DELETE; \
 160      inline int operator*(const Name::Enum&, const int&) MOZ_DELETE; \
 161      inline int operator/(const int&, const Name::Enum&) MOZ_DELETE; \
 162      inline int operator/(const Name::Enum&, const int&) MOZ_DELETE; \
 163      inline int operator%(const int&, const Name::Enum&) MOZ_DELETE; \
 164      inline int operator%(const Name::Enum&, const int&) MOZ_DELETE; \
 165      inline int operator+(const Name::Enum&) MOZ_DELETE; \
 166      inline int operator-(const Name::Enum&) MOZ_DELETE; \
 167      inline int& operator++(Name::Enum&) MOZ_DELETE; \
 168      inline int operator++(Name::Enum&, int) MOZ_DELETE; \
 169      inline int& operator--(Name::Enum&) MOZ_DELETE; \
 170      inline int operator--(Name::Enum&, int) MOZ_DELETE; \
 171      inline bool operator==(const int&, const Name::Enum&) MOZ_DELETE; \
 172      inline bool operator==(const Name::Enum&, const int&) MOZ_DELETE; \
 173      inline bool operator!=(const int&, const Name::Enum&) MOZ_DELETE; \
 174      inline bool operator!=(const Name::Enum&, const int&) MOZ_DELETE; \
 175      inline bool operator>(const int&, const Name::Enum&) MOZ_DELETE; \
 176      inline bool operator>(const Name::Enum&, const int&) MOZ_DELETE; \
 177      inline bool operator<(const int&, const Name::Enum&) MOZ_DELETE; \
 178      inline bool operator<(const Name::Enum&, const int&) MOZ_DELETE; \
 179      inline bool operator>=(const int&, const Name::Enum&) MOZ_DELETE; \
 180      inline bool operator>=(const Name::Enum&, const int&) MOZ_DELETE; \
 181      inline bool operator<=(const int&, const Name::Enum&) MOZ_DELETE; \
 182      inline bool operator<=(const Name::Enum&, const int&) MOZ_DELETE; \
 183      inline bool operator!(const Name::Enum&) MOZ_DELETE; \
 184      inline bool operator&&(const bool&, const Name::Enum&) MOZ_DELETE; \
 185      inline bool operator&&(const Name::Enum&, const bool&) MOZ_DELETE; \
 186      inline bool operator||(const bool&, const Name::Enum&) MOZ_DELETE; \
 187      inline bool operator||(const Name::Enum&, const bool&) MOZ_DELETE; \
 188      inline int operator~(const Name::Enum&) MOZ_DELETE; \
 189      inline int operator&(const int&, const Name::Enum&) MOZ_DELETE; \
 190      inline int operator&(const Name::Enum&, const int&) MOZ_DELETE; \
 191      inline int operator|(const int&, const Name::Enum&) MOZ_DELETE; \
 192      inline int operator|(const Name::Enum&, const int&) MOZ_DELETE; \
 193      inline int operator^(const int&, const Name::Enum&) MOZ_DELETE; \
 194      inline int operator^(const Name::Enum&, const int&) MOZ_DELETE; \
 195      inline int operator<<(const int&, const Name::Enum&) MOZ_DELETE; \
 196      inline int operator<<(const Name::Enum&, const int&) MOZ_DELETE; \
 197      inline int operator>>(const int&, const Name::Enum&) MOZ_DELETE; \
 198      inline int operator>>(const Name::Enum&, const int&) MOZ_DELETE; \
 199      inline int& operator+=(int&, const Name::Enum&) MOZ_DELETE; \
 200      inline int& operator-=(int&, const Name::Enum&) MOZ_DELETE; \
 201      inline int& operator*=(int&, const Name::Enum&) MOZ_DELETE; \
 202      inline int& operator/=(int&, const Name::Enum&) MOZ_DELETE; \
 203      inline int& operator%=(int&, const Name::Enum&) MOZ_DELETE; \
 204      inline int& operator&=(int&, const Name::Enum&) MOZ_DELETE; \
 205      inline int& operator|=(int&, const Name::Enum&) MOZ_DELETE; \
 206      inline int& operator^=(int&, const Name::Enum&) MOZ_DELETE; \
 207      inline int& operator<<=(int&, const Name::Enum&) MOZ_DELETE; \
 208      inline int& operator>>=(int&, const Name::Enum&) MOZ_DELETE;
 209 #endif
 210
 211 #endif /* __cplusplus */
 212
 213 #endif  /* mozilla_TypedEnum_h_ */