mfbt/TypedEnum.h

   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/. */
   6
   7 /* Macros to emulate C++11 typed enums and enum classes. */
   8
   9 #ifndef mozilla_TypedEnum_h
  10 #define mozilla_TypedEnum_h
  11
  12 #include "mozilla/Attributes.h"
  13
  14 #if defined(__cplusplus)
  15
  16 #if defined(__clang__)
  17    /*
  18     * Per Clang documentation, "Note that marketing version numbers should not
  19     * be used to check for language features, as different vendors use different
  20     * numbering schemes. Instead, use the feature checking macros."
  21     */
  22 #  ifndef __has_extension
  23 #    define __has_extension __has_feature /* compatibility, for older versions of clang */
  24 #  endif
  25 #  if __has_extension(cxx_strong_enums)
  26 #    define MOZ_HAVE_CXX11_ENUM_TYPE
  27 #    define MOZ_HAVE_CXX11_STRONG_ENUMS
  28 #  endif
  29 #elif defined(__GNUC__)
  30 #  if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
  31 #    if MOZ_GCC_VERSION_AT_LEAST(4, 6, 3)
  32 #      define MOZ_HAVE_CXX11_ENUM_TYPE
  33 #      define MOZ_HAVE_CXX11_STRONG_ENUMS
  34 #    endif
  35 #  endif
  36 #elif defined(_MSC_VER)
  37 #  if _MSC_VER >= 1400
  38 #    define MOZ_HAVE_CXX11_ENUM_TYPE
  39 #  endif
  40 #  if _MSC_VER >= 1700
  41 #    define MOZ_HAVE_CXX11_STRONG_ENUMS
  42 #  endif
  43 #endif
  44
  45 /**
  46  * MOZ_ENUM_TYPE specifies the underlying numeric type for an enum.  It's
  47  * specified by placing MOZ_ENUM_TYPE(type) immediately after the enum name in
  48  * its declaration, and before the opening curly brace, like
  49  *
  50  *   enum MyEnum MOZ_ENUM_TYPE(uint16_t)
  51  *   {
  52  *     A,
  53  *     B = 7,
  54  *     C
  55  *   };
  56  *
  57  * In supporting compilers, the macro will expand to ": uint16_t".  The
  58  * compiler will allocate exactly two bytes for MyEnum and will require all
  59  * enumerators to have values between 0 and 65535.  (Thus specifying "B =
  60  * 100000" instead of "B = 7" would fail to compile.)  In old compilers the
  61  * macro expands to the empty string, and the underlying type is generally
  62  * undefined.
  63  */
  64 #ifdef MOZ_HAVE_CXX11_ENUM_TYPE
  65 #  define MOZ_ENUM_TYPE(type)   : type
  66 #else
  67 #  define MOZ_ENUM_TYPE(type)   /* no support */
  68 #endif
  69
  70 /**
  71  * MOZ_BEGIN_ENUM_CLASS and MOZ_END_ENUM_CLASS provide access to the
  72  * strongly-typed enumeration feature of C++11 ("enum class").  If supported
  73  * by the compiler, an enum defined using these macros will not be implicitly
  74  * converted to any other type, and its enumerators will be scoped using the
  75  * enumeration name.  Place MOZ_BEGIN_ENUM_CLASS(EnumName [, type]) in place of
  76  * "enum EnumName {", and MOZ_END_ENUM_CLASS(EnumName) in place of the closing
  77  * "};".  For example,
  78  *
  79  *   MOZ_BEGIN_ENUM_CLASS(Enum, int32_t)
  80  *     A,
  81  *     B = 6
  82  *   MOZ_END_ENUM_CLASS(Enum)
  83  *
  84  * This will make "Enum::A" and "Enum::B" appear in the global scope, but "A"
  85  * and "B" will not.  In compilers that support C++11 strongly-typed
  86  * enumerations, implicit conversions of Enum values to numeric types will
  87  * fail.  In other compilers, Enum itself will actually be defined as a class,
  88  * and some implicit conversions will fail while others will succeed.
  89  *
  90  * The optional type argument specifies the underlying type for the enum where
  91  * supported, as with MOZ_ENUM_TYPE().  As with MOZ_ENUM_TYPE(), it will do
  92  * nothing on compilers that do not support it.
  93  *
  94  * MOZ_{BEGIN,END}_ENUM_CLASS doesn't work for defining enum classes nested
  95  * inside classes.  To define an enum class nested inside another class, use
  96  * MOZ_{BEGIN,END}_NESTED_ENUM_CLASS, and place a MOZ_FINISH_NESTED_ENUM_CLASS
  97  * in namespace scope to handle bits that can only be implemented with
  98  * namespace-scoped code.  For example:
  99  *
 100  *   class FooBar {
 101  *
 102  *     MOZ_BEGIN_NESTED_ENUM_CLASS(Enum, int32_t)
 103  *       A,
 104  *       B = 6
 105  *     MOZ_END_NESTED_ENUM_CLASS(Enum)
 106  *
 107  *   };
 108  *
 109  *   MOZ_FINISH_NESTED_ENUM_CLASS(FooBar::Enum)
 110  */
 111 #if defined(MOZ_HAVE_CXX11_STRONG_ENUMS)
 112   /*
 113    * All compilers that support strong enums also support an explicit
 114    * underlying type, so no extra check is needed.
 115    */
 116
 117    /* Single-argument form. */
 118 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER1(Name) \
 119      enum class Name {
 120    /* Two-argument form. */
 121 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER2(Name, type) \
 122      enum class Name : type {
 123 #  define MOZ_END_NESTED_ENUM_CLASS(Name) \
 124      };
 125 #  define MOZ_FINISH_NESTED_ENUM_CLASS(Name) /* nothing */
 126
 127   /*
 128    * MOZ_ENUM_CLASS_ENUM_TYPE allows using enum classes
 129    * as template parameter types. For that, we need integer types.
 130    * In the present case where the compiler supports strong enums,
 131    * these are already integer types so there is nothing more to do.
 132    */
 133 #  define MOZ_ENUM_CLASS_ENUM_TYPE(Name) Name
 134 #else
 135    /**
 136     * We need Name to both name a type, and scope the provided enumerator
 137     * names.  Namespaces and classes both provide scoping, but namespaces
 138     * aren't types, so we need to use a class that wraps the enum values.  We
 139     * have an implicit conversion from the inner enum type to the class, so
 140     * statements like
 141     *
 142     *   Enum x = Enum::A;
 143     *
 144     * will still work.  We need to define an implicit conversion from the class
 145     * to the inner enum as well, so that (for instance) switch statements will
 146     * work.  This means that the class can be implicitly converted to a numeric
 147     * value as well via the enum type, since C++ allows an implicit
 148     * user-defined conversion followed by a standard conversion to still be
 149     * implicit.
 150     *
 151     * We have an explicit constructor from int defined, so that casts like
 152     * (Enum)7 will still work.  We also have a zero-argument constructor with
 153     * no arguments, so declaration without initialization (like "Enum foo;")
 154     * will work.
 155     *
 156     * Additionally, we'll delete as many operators as possible for the inner
 157     * enum type, so statements like this will still fail:
 158     *
 159     *   f(5 + Enum::B); // deleted operator+
 160     *
 161     * But we can't prevent things like this, because C++ doesn't allow
 162     * overriding conversions or assignment operators for enums:
 163     *
 164     *   int x = Enum::A;
 165     *   int f()
 166     *   {
 167     *     return Enum::A;
 168     *   }
 169     */
 170
 171    /* Single-argument form. */
 172 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER1(Name) \
 173      class Name \
 174      { \
 175        public: \
 176          enum Enum \
 177          {
 178    /* Two-argument form. */
 179 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER2(Name, type) \
 180      class Name \
 181      { \
 182        public: \
 183          enum Enum MOZ_ENUM_TYPE(type) \
 184          {
 185 #  define MOZ_END_NESTED_ENUM_CLASS(Name) \
 186          }; \
 187          Name() {} \
 188          Name(Enum aEnum) : mEnum(aEnum) {} \
 189          explicit Name(int num) : mEnum((Enum)num) {} \
 190          operator Enum() const { return mEnum; } \
 191        private: \
 192          Enum mEnum; \
 193      };
 194 #  define MOZ_FINISH_NESTED_ENUM_CLASS(Name) \
 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*(const int&, const Name::Enum&) MOZ_DELETE; \
 200      inline int operator*(const Name::Enum&, const int&) MOZ_DELETE; \
 201      inline int operator/(const int&, const Name::Enum&) MOZ_DELETE; \
 202      inline int operator/(const Name::Enum&, const int&) MOZ_DELETE; \
 203      inline int operator%(const int&, const Name::Enum&) MOZ_DELETE; \
 204      inline int operator%(const Name::Enum&, const int&) MOZ_DELETE; \
 205      inline int operator+(const Name::Enum&) MOZ_DELETE; \
 206      inline int operator-(const Name::Enum&) MOZ_DELETE; \
 207      inline int& operator++(Name::Enum&) MOZ_DELETE; \
 208      inline int operator++(Name::Enum&, int) MOZ_DELETE; \
 209      inline int& operator--(Name::Enum&) MOZ_DELETE; \
 210      inline int operator--(Name::Enum&, int) MOZ_DELETE; \
 211      inline bool operator==(const int&, const Name::Enum&) MOZ_DELETE; \
 212      inline bool operator==(const Name::Enum&, const int&) MOZ_DELETE; \
 213      inline bool operator!=(const int&, const Name::Enum&) MOZ_DELETE; \
 214      inline bool operator!=(const Name::Enum&, const int&) MOZ_DELETE; \
 215      inline bool operator>(const int&, const Name::Enum&) MOZ_DELETE; \
 216      inline bool operator>(const Name::Enum&, const int&) MOZ_DELETE; \
 217      inline bool operator<(const int&, const Name::Enum&) MOZ_DELETE; \
 218      inline bool operator<(const Name::Enum&, const int&) MOZ_DELETE; \
 219      inline bool operator>=(const int&, const Name::Enum&) MOZ_DELETE; \
 220      inline bool operator>=(const Name::Enum&, const int&) MOZ_DELETE; \
 221      inline bool operator<=(const int&, const Name::Enum&) MOZ_DELETE; \
 222      inline bool operator<=(const Name::Enum&, const int&) MOZ_DELETE; \
 223      inline bool operator!(const Name::Enum&) MOZ_DELETE; \
 224      inline bool operator&&(const bool&, const Name::Enum&) MOZ_DELETE; \
 225      inline bool operator&&(const Name::Enum&, const bool&) MOZ_DELETE; \
 226      inline bool operator||(const bool&, const Name::Enum&) MOZ_DELETE; \
 227      inline bool operator||(const Name::Enum&, const bool&) MOZ_DELETE; \
 228      inline int operator~(const Name::Enum&) MOZ_DELETE; \
 229      inline int operator&(const int&, const Name::Enum&) MOZ_DELETE; \
 230      inline int operator&(const Name::Enum&, const int&) MOZ_DELETE; \
 231      inline int operator|(const int&, const Name::Enum&) MOZ_DELETE; \
 232      inline int operator|(const Name::Enum&, const int&) MOZ_DELETE; \
 233      inline int operator^(const int&, const Name::Enum&) MOZ_DELETE; \
 234      inline int operator^(const Name::Enum&, const int&) MOZ_DELETE; \
 235      inline int operator<<(const int&, const Name::Enum&) MOZ_DELETE; \
 236      inline int operator<<(const Name::Enum&, const int&) MOZ_DELETE; \
 237      inline int operator>>(const int&, const Name::Enum&) MOZ_DELETE; \
 238      inline int operator>>(const Name::Enum&, const int&) MOZ_DELETE; \
 239      inline int& operator+=(int&, const Name::Enum&) MOZ_DELETE; \
 240      inline int& operator-=(int&, const Name::Enum&) MOZ_DELETE; \
 241      inline int& operator*=(int&, const Name::Enum&) MOZ_DELETE; \
 242      inline int& operator/=(int&, const Name::Enum&) MOZ_DELETE; \
 243      inline int& operator%=(int&, const Name::Enum&) MOZ_DELETE; \
 244      inline int& operator&=(int&, const Name::Enum&) MOZ_DELETE; \
 245      inline int& operator|=(int&, const Name::Enum&) MOZ_DELETE; \
 246      inline int& operator^=(int&, const Name::Enum&) MOZ_DELETE; \
 247      inline int& operator<<=(int&, const Name::Enum&) MOZ_DELETE; \
 248      inline int& operator>>=(int&, const Name::Enum&) MOZ_DELETE;
 249
 250   /*
 251    * MOZ_ENUM_CLASS_ENUM_TYPE allows using enum classes
 252    * as template parameter types. For that, we need integer types.
 253    * In the present case, the integer type is the Enum nested type.
 254    */
 255 #  define MOZ_ENUM_CLASS_ENUM_TYPE(Name) Name::Enum
 256 #endif
 257
 258    /*
 259     * Count the number of arguments passed to MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS,
 260     * very carefully tiptoeing around an MSVC bug where it improperly expands
 261     * __VA_ARGS__ as a single token in argument lists. See these URLs for
 262     * details:
 263     *
 264     *   http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement
 265     *   http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644
 266     */
 267 #  define MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS_IMPL2(_1, _2, count, ...) \
 268      count
 269 #  define MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS_IMPL(args) \
 270      MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS_IMPL2 args
 271 #  define MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS(...) \
 272      MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS_IMPL((__VA_ARGS__, 2, 1, 0))
 273    /* Pick the right helper macro to invoke. */
 274 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER2(count) \
 275     MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER##count
 276 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER1(count) \
 277      MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER2(count)
 278 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER(count) \
 279      MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER1(count)
 280    /* The actual macro. */
 281 #  define MOZ_BEGIN_NESTED_ENUM_CLASS_GLUE(x, y) x y
 282 #  define MOZ_BEGIN_NESTED_ENUM_CLASS(...) \
 283      MOZ_BEGIN_NESTED_ENUM_CLASS_GLUE(MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER(MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS(__VA_ARGS__)), \
 284                                       (__VA_ARGS__))
 285
 286 #  define MOZ_BEGIN_ENUM_CLASS(...) MOZ_BEGIN_NESTED_ENUM_CLASS(__VA_ARGS__)
 287 #  define MOZ_END_ENUM_CLASS(Name) \
 288      MOZ_END_NESTED_ENUM_CLASS(Name) \
 289      MOZ_FINISH_NESTED_ENUM_CLASS(Name)
 290
 291 #endif /* __cplusplus */
 292
 293 #endif /* mozilla_TypedEnum_h */