1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/mfbt/TypedEnumInternal.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,112 @@
1.4 +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
1.5 +/* vim: set ts=8 sts=2 et sw=2 tw=80: */
1.6 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.7 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.8 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.9 +
1.10 +/* Internal stuff needed by TypedEnum.h and TypedEnumBits.h. */
1.11 +
1.12 +// NOTE: When we can assume C++11 enum class support and TypedEnum.h goes away,
1.13 +// we should then consider folding TypedEnumInternal.h into TypedEnumBits.h.
1.14 +
1.15 +#ifndef mozilla_TypedEnumInternal_h
1.16 +#define mozilla_TypedEnumInternal_h
1.17 +
1.18 +#include "mozilla/Attributes.h"
1.19 +
1.20 +#if defined(__cplusplus)
1.21 +
1.22 +#if defined(__clang__)
1.23 + /*
1.24 + * Per Clang documentation, "Note that marketing version numbers should not
1.25 + * be used to check for language features, as different vendors use different
1.26 + * numbering schemes. Instead, use the feature checking macros."
1.27 + */
1.28 +# ifndef __has_extension
1.29 +# define __has_extension __has_feature /* compatibility, for older versions of clang */
1.30 +# endif
1.31 +# if __has_extension(cxx_strong_enums)
1.32 +# define MOZ_HAVE_CXX11_ENUM_TYPE
1.33 +# define MOZ_HAVE_CXX11_STRONG_ENUMS
1.34 +# endif
1.35 +#elif defined(__GNUC__)
1.36 +# if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
1.37 +# if MOZ_GCC_VERSION_AT_LEAST(4, 6, 3)
1.38 +# define MOZ_HAVE_CXX11_ENUM_TYPE
1.39 +# define MOZ_HAVE_CXX11_STRONG_ENUMS
1.40 +# endif
1.41 +# endif
1.42 +#elif defined(_MSC_VER)
1.43 +# if _MSC_VER >= 1400
1.44 +# define MOZ_HAVE_CXX11_ENUM_TYPE
1.45 +# endif
1.46 +# if _MSC_VER >= 1700
1.47 +# define MOZ_HAVE_CXX11_STRONG_ENUMS
1.48 +# endif
1.49 +#endif
1.50 +
1.51 +namespace mozilla {
1.52 +
1.53 +/*
1.54 + * The problem that CastableTypedEnumResult aims to solve is that
1.55 + * typed enums are not convertible to bool, and there is no way to make them
1.56 + * be, yet user code wants to be able to write
1.57 + *
1.58 + * if (myFlags & Flags::SOME_PARTICULAR_FLAG) (1)
1.59 + *
1.60 + * There are different approaches to solving this. Most of them require
1.61 + * adapting user code. For example, we could implement operator! and have
1.62 + * the user write
1.63 + *
1.64 + * if (!!(myFlags & Flags::SOME_PARTICULAR_FLAG)) (2)
1.65 + *
1.66 + * Or we could supply a IsNonZero() or Any() function returning whether
1.67 + * an enum value is nonzero, and have the user write
1.68 + *
1.69 + * if (Any(Flags & Flags::SOME_PARTICULAR_FLAG)) (3)
1.70 + *
1.71 + * But instead, we choose to preserve the original user syntax (1) as it
1.72 + * is inherently more readable, and to ease porting existing code to typed
1.73 + * enums. We achieve this by having operator& and other binary bitwise
1.74 + * operators have as return type a class, CastableTypedEnumResult,
1.75 + * that wraps a typed enum but adds bool convertibility.
1.76 + */
1.77 +template<typename E>
1.78 +class CastableTypedEnumResult
1.79 +{
1.80 + private:
1.81 + const E mValue;
1.82 +
1.83 + public:
1.84 + explicit MOZ_CONSTEXPR CastableTypedEnumResult(E value)
1.85 + : mValue(value)
1.86 + {}
1.87 +
1.88 + MOZ_CONSTEXPR operator E() const { return mValue; }
1.89 +
1.90 + template<typename DestinationType>
1.91 + MOZ_EXPLICIT_CONVERSION MOZ_CONSTEXPR
1.92 + operator DestinationType() const {
1.93 + return DestinationType(mValue);
1.94 + }
1.95 +
1.96 + MOZ_CONSTEXPR bool operator !() const { return !bool(mValue); }
1.97 +
1.98 +#ifndef MOZ_HAVE_CXX11_STRONG_ENUMS
1.99 + // This get() method is used to implement a constructor in the
1.100 + // non-c++11 fallback path for MOZ_BEGIN_ENUM_CLASS, taking a
1.101 + // CastableTypedEnumResult. If we try to implement it using the
1.102 + // above conversion operator E(), then at least clang 3.3
1.103 + // (when forced to take the non-c++11 fallback path) compiles
1.104 + // this constructor to an infinite recursion. So we introduce this
1.105 + // get() method, that does exactly the same as the conversion operator,
1.106 + // to work around this.
1.107 + MOZ_CONSTEXPR E get() const { return mValue; }
1.108 +#endif
1.109 +};
1.110 +
1.111 +} // namespace mozilla
1.112 +
1.113 +#endif // __cplusplus
1.114 +
1.115 +#endif // mozilla_TypedEnumInternal_h
