Extracted BOOST_EXPLICIT_OPERATOR_BOOL macro from Boost.Log.

[SVN r85543]

include/boost/utility/explicit_operator_bool.hpp

@@ -0,0 +1,128 @@
+/*
+ *          Copyright Andrey Semashev 2007 - 2013.
+ * Distributed under the Boost Software License, Version 1.0.
+ *    (See accompanying file LICENSE_1_0.txt or copy at
+ *          http://www.boost.org/LICENSE_1_0.txt)
+ */
+/*!
+ * \file   explicit_operator_bool.hpp
+ * \author Andrey Semashev
+ * \date   08.03.2009
+ *
+ * This header defines a compatibility macro that implements an unspecified
+ * \c bool operator idiom, which is superseded with explicit conversion operators in
+ * C++11.
+ */
+
+#ifndef BOOST_UTILITY_EXPLICIT_OPERATOR_BOOL_HPP_INCLUDED_
+#define BOOST_UTILITY_EXPLICIT_OPERATOR_BOOL_HPP_INCLUDED_
+
+#include <boost/config.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+#if !defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS)
+
+/*!
+ * \brief The macro defines an explicit operator of conversion to \c bool
+ *
+ * The macro should be used inside the definition of a class that has to
+ * support the conversion. The class should also implement <tt>operator!</tt>,
+ * in terms of which the conversion operator will be implemented.
+ */
+#define BOOST_EXPLICIT_OPERATOR_BOOL()\
+    BOOST_FORCEINLINE explicit operator bool () const\
+    {\
+        return !this->operator! ();\
+    }
+
+/*!
+ * \brief The macro defines a constexpr explicit operator of conversion to \c bool
+ *
+ * The macro should be used inside the definition of a class that has to
+ * support the conversion. The class should also implement <tt>operator!</tt>,
+ * in terms of which the conversion operator will be implemented.
+ */
+#define BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()\
+    BOOST_FORCEINLINE BOOST_CONSTEXPR explicit operator bool () const\
+    {\
+        return !this->operator! ();\
+    }
+
+#else // !defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS)
+
+#if (defined(__SUNPRO_CC) && (__SUNPRO_CC <= 0x530)) && !defined(BOOST_NO_COMPILER_CONFIG)
+// Sun C++ 5.3 can't handle the safe_bool idiom, so don't use it
+#define BOOST_NO_UNSPECIFIED_BOOL
+#endif // (defined(__SUNPRO_CC) && (__SUNPRO_CC <= 0x530)) && !defined(BOOST_NO_COMPILER_CONFIG)
+
+#if !defined(BOOST_NO_UNSPECIFIED_BOOL)
+
+namespace boost {
+
+namespace detail {
+
+#if !defined(_MSC_VER)
+
+    struct unspecified_bool
+    {
+        // NOTE TO THE USER: If you see this in error messages then you tried
+        // to apply an unsupported operator on the object that supports
+        // explicit conversion to bool.
+        struct OPERATORS_NOT_ALLOWED;
+        static void true_value(OPERATORS_NOT_ALLOWED*) {}
+    };
+    typedef void (*unspecified_bool_type)(unspecified_bool::OPERATORS_NOT_ALLOWED*);
+
+#else
+
+    // MSVC is too eager to convert pointer to function to void* even though it shouldn't
+    struct unspecified_bool
+    {
+        // NOTE TO THE USER: If you see this in error messages then you tried
+        // to apply an unsupported operator on the object that supports
+        // explicit conversion to bool.
+        struct OPERATORS_NOT_ALLOWED;
+        void true_value(OPERATORS_NOT_ALLOWED*) {}
+    };
+    typedef void (unspecified_bool::*unspecified_bool_type)(unspecified_bool::OPERATORS_NOT_ALLOWED*);
+
+#endif
+
+} // namespace detail
+
+} // namespace boost
+
+#define BOOST_EXPLICIT_OPERATOR_BOOL()\
+    BOOST_FORCEINLINE operator boost::detail::unspecified_bool_type () const\
+    {\
+        return (!this->operator! () ? &boost::detail::unspecified_bool::true_value : (boost::detail::unspecified_bool_type)0);\
+    }
+
+#define BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()\
+    BOOST_FORCEINLINE BOOST_CONSTEXPR operator boost::detail::unspecified_bool_type () const\
+    {\
+        return (!this->operator! () ? &boost::detail::unspecified_bool::true_value : (boost::detail::unspecified_bool_type)0);\
+    }
+
+#else // !defined(BOOST_NO_UNSPECIFIED_BOOL)
+
+#define BOOST_EXPLICIT_OPERATOR_BOOL()\
+    BOOST_FORCEINLINE operator bool () const\
+    {\
+        return !this->operator! ();\
+    }
+
+#define BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()\
+    BOOST_FORCEINLINE BOOST_CONSTEXPR operator bool () const\
+    {\
+        return !this->operator! ();\
+    }
+
+#endif // !defined(BOOST_NO_UNSPECIFIED_BOOL)
+
+#endif // !defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS)
+
+#endif // BOOST_UTILITY_EXPLICIT_OPERATOR_BOOL_HPP_INCLUDED_