Chris@16: // Three-state boolean logic library
Chris@16: 
Chris@16: // Copyright Douglas Gregor 2002-2004. Use, modification and
Chris@16: // distribution is subject to the Boost Software License, Version
Chris@16: // 1.0. (See accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: 
Chris@16: // For more information, see http://www.boost.org
Chris@16: #ifndef BOOST_LOGIC_TRIBOOL_HPP
Chris@16: #define BOOST_LOGIC_TRIBOOL_HPP
Chris@16: 
Chris@16: #include <boost/logic/tribool_fwd.hpp>
Chris@16: #include <boost/config.hpp>
Chris@16: #include <boost/detail/workaround.hpp>
Chris@16: 
Chris@101: #ifdef BOOST_HAS_PRAGMA_ONCE
Chris@16: #  pragma once
Chris@16: #endif
Chris@16: 
Chris@16: namespace boost { namespace logic {
Chris@16: 
Chris@16: /// INTERNAL ONLY
Chris@16: namespace detail {
Chris@16: /**
Chris@16:  * INTERNAL ONLY
Chris@16:  *
Chris@16:  * \brief A type used only to uniquely identify the 'indeterminate'
Chris@16:  * function/keyword.
Chris@16:  */
Chris@16: struct indeterminate_t
Chris@16: {
Chris@16: #if BOOST_WORKAROUND(__BORLANDC__, < 0x0600)
Chris@16:   char dummy_; // BCB would use 8 bytes by default
Chris@16: #endif
Chris@16: };
Chris@16: 
Chris@16: } // end namespace detail
Chris@16: 
Chris@16: /**
Chris@16:  * INTERNAL ONLY
Chris@16:  * The type of the 'indeterminate' keyword. This has the same type as the
Chris@16:  * function 'indeterminate' so that we can recognize when the keyword is
Chris@16:  * used.
Chris@16:  */
Chris@16: typedef bool (*indeterminate_keyword_t)(tribool, detail::indeterminate_t);
Chris@16: 
Chris@16: /**
Chris@16:  * \brief Keyword and test function for the indeterminate tribool value
Chris@16:  *
Chris@16:  * The \c indeterminate function has a dual role. It's first role is
Chris@16:  * as a unary function that tells whether the tribool value is in the
Chris@16:  * "indeterminate" state. It's second role is as a keyword
Chris@16:  * representing the indeterminate (just like "true" and "false"
Chris@16:  * represent the true and false states). If you do not like the name
Chris@16:  * "indeterminate", and would prefer to use a different name, see the
Chris@16:  * macro \c BOOST_TRIBOOL_THIRD_STATE.
Chris@16:  *
Chris@16:  * \returns <tt>x.value == tribool::indeterminate_value</tt>
Chris@16:  * \throws nothrow
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline bool
Chris@16: indeterminate(tribool x,
Chris@101:               detail::indeterminate_t dummy = detail::indeterminate_t()) BOOST_NOEXCEPT;
Chris@16: 
Chris@16: /**
Chris@16:  * \brief A 3-state boolean type.
Chris@16:  *
Chris@16:  * 3-state boolean values are either true, false, or
Chris@16:  * indeterminate.
Chris@16:  */
Chris@16: class tribool
Chris@16: {
Chris@16: private:
Chris@16:   /// INTERNAL ONLY
Chris@16:   struct dummy {
Chris@16:     void nonnull() {};
Chris@16:   };
Chris@16: 
Chris@16:   typedef void (dummy::*safe_bool)();
Chris@16: 
Chris@16: public:
Chris@16:   /**
Chris@16:    * Construct a new 3-state boolean value with the value 'false'.
Chris@16:    *
Chris@16:    * \throws nothrow
Chris@16:    */
Chris@101:   BOOST_CONSTEXPR tribool() BOOST_NOEXCEPT : value(false_value) {}
Chris@16: 
Chris@16:   /**
Chris@16:    * Construct a new 3-state boolean value with the given boolean
Chris@16:    * value, which may be \c true or \c false.
Chris@16:    *
Chris@16:    * \throws nothrow
Chris@16:    */
Chris@101:   BOOST_CONSTEXPR tribool(bool initial_value) BOOST_NOEXCEPT : value(initial_value? true_value : false_value) {}
Chris@16: 
Chris@16:   /**
Chris@16:    * Construct a new 3-state boolean value with an indeterminate value.
Chris@16:    *
Chris@16:    * \throws nothrow
Chris@16:    */
Chris@101:   BOOST_CONSTEXPR tribool(indeterminate_keyword_t) BOOST_NOEXCEPT : value(indeterminate_value) {}
Chris@16: 
Chris@16:   /**
Chris@16:    * Use a 3-state boolean in a boolean context. Will evaluate true in a
Chris@16:    * boolean context only when the 3-state boolean is definitely true.
Chris@16:    *
Chris@16:    * \returns true if the 3-state boolean is true, false otherwise
Chris@16:    * \throws nothrow
Chris@16:    */
Chris@101:   BOOST_CONSTEXPR operator safe_bool() const BOOST_NOEXCEPT
Chris@16:   {
Chris@16:     return value == true_value? &dummy::nonnull : 0;
Chris@16:   }
Chris@16: 
Chris@16:   /**
Chris@16:    * The actual stored value in this 3-state boolean, which may be false, true,
Chris@16:    * or indeterminate.
Chris@16:    */
Chris@16:   enum value_t { false_value, true_value, indeterminate_value } value;
Chris@16: };
Chris@16: 
Chris@16: // Check if the given tribool has an indeterminate value. Also doubles as a
Chris@16: // keyword for the 'indeterminate' value
Chris@101: BOOST_CONSTEXPR inline bool indeterminate(tribool x, detail::indeterminate_t) BOOST_NOEXCEPT
Chris@16: {
Chris@16:   return x.value == tribool::indeterminate_value;
Chris@16: }
Chris@16: 
Chris@16: /** @defgroup logical Logical operations
Chris@16:  */
Chris@16: //@{
Chris@16: /**
Chris@16:  * \brief Computes the logical negation of a tribool
Chris@16:  *
Chris@16:  * \returns the logical negation of the tribool, according to the
Chris@16:  * table:
Chris@16:  *  <table border=1>
Chris@16:  *    <tr>
Chris@16:  *      <th><center><code>!</code></center></th>
Chris@16:  *      <th/>
Chris@16:  *    </tr>
Chris@16:  *    <tr>
Chris@16:  *      <th><center>false</center></th>
Chris@16:  *      <td><center>true</center></td>
Chris@16:  *    </tr>
Chris@16:  *    <tr>
Chris@16:  *      <th><center>true</center></th>
Chris@16:  *      <td><center>false</center></td>
Chris@16:  *    </tr>
Chris@16:  *    <tr>
Chris@16:  *      <th><center>indeterminate</center></th>
Chris@16:  *      <td><center>indeterminate</center></td>
Chris@16:  *    </tr>
Chris@16:  *  </table>
Chris@16:  * \throws nothrow
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator!(tribool x) BOOST_NOEXCEPT
Chris@16: {
Chris@16:   return x.value == tribool::false_value? tribool(true)
Chris@16:         :x.value == tribool::true_value? tribool(false)
Chris@16:         :tribool(indeterminate);
Chris@16: }
Chris@16: 
Chris@16: /**
Chris@16:  * \brief Computes the logical conjuction of two tribools
Chris@16:  *
Chris@16:  * \returns the result of logically ANDing the two tribool values,
Chris@16:  * according to the following table:
Chris@16:  *       <table border=1>
Chris@16:  *           <tr>
Chris@16:  *             <th><center><code>&amp;&amp;</code></center></th>
Chris@16:  *             <th><center>false</center></th>
Chris@16:  *             <th><center>true</center></th>
Chris@16:  *             <th><center>indeterminate</center></th>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>false</center></th>
Chris@16:  *             <td><center>false</center></td>
Chris@16:  *             <td><center>false</center></td>
Chris@16:  *             <td><center>false</center></td>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>true</center></th>
Chris@16:  *             <td><center>false</center></td>
Chris@16:  *             <td><center>true</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>indeterminate</center></th>
Chris@16:  *             <td><center>false</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *           </tr>
Chris@16:  *       </table>
Chris@16:  * \throws nothrow
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator&&(tribool x, tribool y) BOOST_NOEXCEPT
Chris@16: {
Chris@101:   return (static_cast<bool>(!x) || static_cast<bool>(!y))
Chris@101:     ? tribool(false)
Chris@101:     : ((static_cast<bool>(x) && static_cast<bool>(y)) ? tribool(true) : indeterminate)
Chris@101:   ;
Chris@16: }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator&&(tribool x, bool y) BOOST_NOEXCEPT
Chris@16: { return y? x : tribool(false); }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator&&(bool x, tribool y) BOOST_NOEXCEPT
Chris@16: { return x? y : tribool(false); }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator&&(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
Chris@16: { return !x? tribool(false) : tribool(indeterminate); }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator&&(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
Chris@16: { return !x? tribool(false) : tribool(indeterminate); }
Chris@16: 
Chris@16: /**
Chris@16:  * \brief Computes the logical disjunction of two tribools
Chris@16:  *
Chris@16:  * \returns the result of logically ORing the two tribool values,
Chris@16:  * according to the following table:
Chris@16:  *       <table border=1>
Chris@16:  *           <tr>
Chris@16:  *             <th><center><code>||</code></center></th>
Chris@16:  *             <th><center>false</center></th>
Chris@16:  *             <th><center>true</center></th>
Chris@16:  *             <th><center>indeterminate</center></th>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>false</center></th>
Chris@16:  *             <td><center>false</center></td>
Chris@16:  *             <td><center>true</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>true</center></th>
Chris@16:  *             <td><center>true</center></td>
Chris@16:  *             <td><center>true</center></td>
Chris@16:  *             <td><center>true</center></td>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>indeterminate</center></th>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *             <td><center>true</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *           </tr>
Chris@16:  *       </table>
Chris@16:  *  \throws nothrow
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator||(tribool x, tribool y) BOOST_NOEXCEPT
Chris@16: {
Chris@101:   return (static_cast<bool>(!x) && static_cast<bool>(!y))
Chris@101:     ? tribool(false)
Chris@101:     : ((static_cast<bool>(x) || static_cast<bool>(y)) ? tribool(true) : tribool(indeterminate))
Chris@101:   ;
Chris@16: }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator||(tribool x, bool y) BOOST_NOEXCEPT
Chris@16: { return y? tribool(true) : x; }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator||(bool x, tribool y) BOOST_NOEXCEPT
Chris@16: { return x? tribool(true) : y; }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator||(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
Chris@16: { return x? tribool(true) : tribool(indeterminate); }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator||(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
Chris@16: { return x? tribool(true) : tribool(indeterminate); }
Chris@16: //@}
Chris@16: 
Chris@16: /**
Chris@16:  * \brief Compare tribools for equality
Chris@16:  *
Chris@16:  * \returns the result of comparing two tribool values, according to
Chris@16:  * the following table:
Chris@16:  *       <table border=1>
Chris@16:  *          <tr>
Chris@16:  *            <th><center><code>==</code></center></th>
Chris@16:  *            <th><center>false</center></th>
Chris@16:  *            <th><center>true</center></th>
Chris@16:  *            <th><center>indeterminate</center></th>
Chris@16:  *          </tr>
Chris@16:  *          <tr>
Chris@16:  *            <th><center>false</center></th>
Chris@16:  *            <td><center>true</center></td>
Chris@16:  *            <td><center>false</center></td>
Chris@16:  *            <td><center>indeterminate</center></td>
Chris@16:  *          </tr>
Chris@16:  *          <tr>
Chris@16:  *            <th><center>true</center></th>
Chris@16:  *            <td><center>false</center></td>
Chris@16:  *            <td><center>true</center></td>
Chris@16:  *            <td><center>indeterminate</center></td>
Chris@16:  *          </tr>
Chris@16:  *          <tr>
Chris@16:  *            <th><center>indeterminate</center></th>
Chris@16:  *            <td><center>indeterminate</center></td>
Chris@16:  *            <td><center>indeterminate</center></td>
Chris@16:  *            <td><center>indeterminate</center></td>
Chris@16:  *          </tr>
Chris@16:  *      </table>
Chris@16:  * \throws nothrow
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator==(tribool x, tribool y) BOOST_NOEXCEPT
Chris@16: {
Chris@101:   return (indeterminate(x) || indeterminate(y))
Chris@101:     ? indeterminate
Chris@101:     : ((x && y) || (!x && !y))
Chris@101:   ;
Chris@16: }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator==(tribool x, bool y) BOOST_NOEXCEPT { return x == tribool(y); }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator==(bool x, tribool y) BOOST_NOEXCEPT { return tribool(x) == y; }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator==(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
Chris@16: { return tribool(indeterminate) == x; }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator==(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
Chris@16: { return tribool(indeterminate) == x; }
Chris@16: 
Chris@16: /**
Chris@16:  * \brief Compare tribools for inequality
Chris@16:  *
Chris@16:  * \returns the result of comparing two tribool values for inequality,
Chris@16:  * according to the following table:
Chris@16:  *       <table border=1>
Chris@16:  *           <tr>
Chris@16:  *             <th><center><code>!=</code></center></th>
Chris@16:  *             <th><center>false</center></th>
Chris@16:  *             <th><center>true</center></th>
Chris@16:  *             <th><center>indeterminate</center></th>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>false</center></th>
Chris@16:  *             <td><center>false</center></td>
Chris@16:  *             <td><center>true</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>true</center></th>
Chris@16:  *             <td><center>true</center></td>
Chris@16:  *             <td><center>false</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *           </tr>
Chris@16:  *           <tr>
Chris@16:  *             <th><center>indeterminate</center></th>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *             <td><center>indeterminate</center></td>
Chris@16:  *           </tr>
Chris@16:  *       </table>
Chris@16:  * \throws nothrow
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator!=(tribool x, tribool y) BOOST_NOEXCEPT
Chris@16: {
Chris@101:   return (indeterminate(x) || indeterminate(y))
Chris@101:     ? indeterminate
Chris@101:     : !((x && y) || (!x && !y))
Chris@101:   ;
Chris@16: }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator!=(tribool x, bool y) BOOST_NOEXCEPT { return x != tribool(y); }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator!=(bool x, tribool y) BOOST_NOEXCEPT { return tribool(x) != y; }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator!=(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
Chris@16: { return tribool(indeterminate) != x; }
Chris@16: 
Chris@16: /**
Chris@16:  * \overload
Chris@16:  */
Chris@101: BOOST_CONSTEXPR inline tribool operator!=(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
Chris@16: { return x != tribool(indeterminate); }
Chris@16: 
Chris@16: } } // end namespace boost::logic
Chris@16: 
Chris@16: // Pull tribool and indeterminate into namespace "boost"
Chris@16: namespace boost {
Chris@16:   using logic::tribool;
Chris@16:   using logic::indeterminate;
Chris@16: }
Chris@16: 
Chris@16: /**
Chris@16:  * \brief Declare a new name for the third state of a tribool
Chris@16:  *
Chris@16:  * Use this macro to declare a new name for the third state of a
Chris@16:  * tribool. This state can have any number of new names (in addition
Chris@16:  * to \c indeterminate), all of which will be equivalent. The new name will be
Chris@16:  * placed in the namespace in which the macro is expanded.
Chris@16:  *
Chris@16:  * Example:
Chris@16:  *   BOOST_TRIBOOL_THIRD_STATE(true_or_false)
Chris@16:  *
Chris@16:  *   tribool x(true_or_false);
Chris@16:  *   // potentially set x
Chris@16:  *   if (true_or_false(x)) {
Chris@16:  *     // don't know what x is
Chris@16:  *   }
Chris@16:  */
Chris@16: #define BOOST_TRIBOOL_THIRD_STATE(Name)                                 \
Chris@16: inline bool                                                             \
Chris@16: Name(boost::logic::tribool x,                                           \
Chris@16:      boost::logic::detail::indeterminate_t =                            \
Chris@16:        boost::logic::detail::indeterminate_t())                         \
Chris@16: { return x.value == boost::logic::tribool::indeterminate_value; }
Chris@16: 
Chris@16: #endif // BOOST_LOGIC_TRIBOOL_HPP
Chris@16: