michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ts=8 sts=2 et sw=2 tw=80: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: /* Internal stuff needed by TypedEnum.h and TypedEnumBits.h. */
michael@0: 
michael@0: // NOTE: When we can assume C++11 enum class support and TypedEnum.h goes away,
michael@0: // we should then consider folding TypedEnumInternal.h into TypedEnumBits.h.
michael@0: 
michael@0: #ifndef mozilla_TypedEnumInternal_h
michael@0: #define mozilla_TypedEnumInternal_h
michael@0: 
michael@0: #include "mozilla/Attributes.h"
michael@0: 
michael@0: #if defined(__cplusplus)
michael@0: 
michael@0: #if defined(__clang__)
michael@0:    /*
michael@0:     * Per Clang documentation, "Note that marketing version numbers should not
michael@0:     * be used to check for language features, as different vendors use different
michael@0:     * numbering schemes. Instead, use the feature checking macros."
michael@0:     */
michael@0: #  ifndef __has_extension
michael@0: #    define __has_extension __has_feature /* compatibility, for older versions of clang */
michael@0: #  endif
michael@0: #  if __has_extension(cxx_strong_enums)
michael@0: #    define MOZ_HAVE_CXX11_ENUM_TYPE
michael@0: #    define MOZ_HAVE_CXX11_STRONG_ENUMS
michael@0: #  endif
michael@0: #elif defined(__GNUC__)
michael@0: #  if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
michael@0: #    if MOZ_GCC_VERSION_AT_LEAST(4, 6, 3)
michael@0: #      define MOZ_HAVE_CXX11_ENUM_TYPE
michael@0: #      define MOZ_HAVE_CXX11_STRONG_ENUMS
michael@0: #    endif
michael@0: #  endif
michael@0: #elif defined(_MSC_VER)
michael@0: #  if _MSC_VER >= 1400
michael@0: #    define MOZ_HAVE_CXX11_ENUM_TYPE
michael@0: #  endif
michael@0: #  if _MSC_VER >= 1700
michael@0: #    define MOZ_HAVE_CXX11_STRONG_ENUMS
michael@0: #  endif
michael@0: #endif
michael@0: 
michael@0: namespace mozilla {
michael@0: 
michael@0: /*
michael@0:  * The problem that CastableTypedEnumResult aims to solve is that
michael@0:  * typed enums are not convertible to bool, and there is no way to make them
michael@0:  * be, yet user code wants to be able to write
michael@0:  *
michael@0:  *   if (myFlags & Flags::SOME_PARTICULAR_FLAG)              (1)
michael@0:  *
michael@0:  * There are different approaches to solving this. Most of them require
michael@0:  * adapting user code. For example, we could implement operator! and have
michael@0:  * the user write
michael@0:  *
michael@0:  *   if (!!(myFlags & Flags::SOME_PARTICULAR_FLAG))          (2)
michael@0:  *
michael@0:  * Or we could supply a IsNonZero() or Any() function returning whether
michael@0:  * an enum value is nonzero, and have the user write
michael@0:  *
michael@0:  *   if (Any(Flags & Flags::SOME_PARTICULAR_FLAG))           (3)
michael@0:  *
michael@0:  * But instead, we choose to preserve the original user syntax (1) as it
michael@0:  * is inherently more readable, and to ease porting existing code to typed
michael@0:  * enums. We achieve this by having operator& and other binary bitwise
michael@0:  * operators have as return type a class, CastableTypedEnumResult,
michael@0:  * that wraps a typed enum but adds bool convertibility.
michael@0:  */
michael@0: template<typename E>
michael@0: class CastableTypedEnumResult
michael@0: {
michael@0:   private:
michael@0:     const E mValue;
michael@0: 
michael@0:   public:
michael@0:     explicit MOZ_CONSTEXPR CastableTypedEnumResult(E value)
michael@0:       : mValue(value)
michael@0:     {}
michael@0: 
michael@0:     MOZ_CONSTEXPR operator E() const { return mValue; }
michael@0: 
michael@0:     template<typename DestinationType>
michael@0:     MOZ_EXPLICIT_CONVERSION MOZ_CONSTEXPR
michael@0:     operator DestinationType() const {
michael@0:       return DestinationType(mValue);
michael@0:     }
michael@0: 
michael@0:     MOZ_CONSTEXPR bool operator !() const { return !bool(mValue); }
michael@0: 
michael@0: #ifndef MOZ_HAVE_CXX11_STRONG_ENUMS
michael@0:     // This get() method is used to implement a constructor in the
michael@0:     // non-c++11 fallback path for MOZ_BEGIN_ENUM_CLASS, taking a
michael@0:     // CastableTypedEnumResult. If we try to implement it using the
michael@0:     // above conversion operator E(), then at least clang 3.3
michael@0:     // (when forced to take the non-c++11 fallback path) compiles
michael@0:     // this constructor to an infinite recursion. So we introduce this
michael@0:     // get() method, that does exactly the same as the conversion operator,
michael@0:     // to work around this.
michael@0:     MOZ_CONSTEXPR E get() const { return mValue; }
michael@0: #endif
michael@0: };
michael@0: 
michael@0: } // namespace mozilla
michael@0: 
michael@0: #endif // __cplusplus
michael@0: 
michael@0: #endif // mozilla_TypedEnumInternal_h