gecko-dev/mfbt/TypedEnum.h

/* -*- 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/Attributes.h"

#if defined(__cplusplus)

#if defined(__clang__)
   /*
    * Per Clang documentation, "Note that marketing version numbers should not
    * be used to check for language features, as different vendors use different
    * numbering schemes. Instead, use the feature checking macros."
    */
#  ifndef __has_extension
#    define __has_extension __has_feature /* compatibility, for older versions of clang */
#  endif
#  if __has_extension(cxx_strong_enums)
#    define MOZ_HAVE_CXX11_ENUM_TYPE
#    define MOZ_HAVE_CXX11_STRONG_ENUMS
#  endif
#elif defined(__GNUC__)
#  if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
#    if MOZ_GCC_VERSION_AT_LEAST(4, 5, 1)
#      define MOZ_HAVE_CXX11_ENUM_TYPE
#      define MOZ_HAVE_CXX11_STRONG_ENUMS
#    endif
#  endif
#elif defined(_MSC_VER)
#  if _MSC_VER >= 1400
#    define MOZ_HAVE_CXX11_ENUM_TYPE
#  endif
#  if _MSC_VER >= 1700
#    define MOZ_HAVE_CXX11_STRONG_ENUMS
#  endif
#endif

/**
 * 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 type argument specifies the underlying type for the enum where
 * supported, as with MOZ_ENUM_TYPE().  For simplicity, it is currently
 * mandatory.  As with MOZ_ENUM_TYPE(), it will do nothing on compilers that do
 * not support it.
 *
 * Note that the workaround implemented here is not compatible with enums
 * nested inside a class.
 */
#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.
   */
#  define MOZ_BEGIN_ENUM_CLASS(Name, type) enum class Name : type {
#  define MOZ_END_ENUM_CLASS(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;
    *   }
    */
#  define MOZ_BEGIN_ENUM_CLASS(Name, type) \
     class Name \
     { \
       public: \
         enum Enum MOZ_ENUM_TYPE(type) \
         {
#  define MOZ_END_ENUM_CLASS(Name) \
         }; \
         Name() {} \
         Name(Enum aEnum) : mEnum(aEnum) {} \
         explicit Name(int num) : mEnum((Enum)num) {} \
         operator Enum() const { return mEnum; } \
       private: \
         Enum mEnum; \
     }; \
     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 Name::Enum&) 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;
#endif

#endif /* __cplusplus */

#endif /* mozilla_TypedEnum_h */