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gecko-dev/mfbt/TypedEnum.h

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/* -*- 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, 6, 3)
# 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 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() {} \
Name(Enum aEnum) : mEnum(aEnum) {} \
explicit Name(int num) : mEnum((Enum)num) {} \
operator Enum() const { return mEnum; } \
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 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;
/*
* 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
/*
* Count the number of arguments passed to MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS,
* very carefully tiptoeing around an MSVC bug where it improperly expands
* __VA_ARGS__ as a single token in argument lists. See these URLs for
* details:
*
* http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement
* http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644
*/
# define MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS_IMPL2(_1, _2, count, ...) \
count
# define MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS_IMPL(args) \
MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS_IMPL2 args
# define MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS(...) \
MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS_IMPL((__VA_ARGS__, 2, 1, 0))
/* Pick the right helper macro to invoke. */
# define MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER2(count) \
MOZ_BEGIN_NESTED_ENUM_CLASS_HELPER##count
# define MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER1(count) \
MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER2(count)
# define MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER(count) \
MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER1(count)
/* The actual macro. */
# define MOZ_BEGIN_NESTED_ENUM_CLASS_GLUE(x, y) x y
# define MOZ_BEGIN_NESTED_ENUM_CLASS(...) \
MOZ_BEGIN_NESTED_ENUM_CLASS_GLUE(MOZ_BEGIN_NESTED_ENUM_CLASS_CHOOSE_HELPER(MOZ_COUNT_BEGIN_ENUM_CLASS_ARGS(__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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