// Three-state boolean logic library // Copyright Douglas Gregor 2002-2004. Use, modification and // distribution is subject to 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) // For more information, see http://www.boost.org #ifndef BOOST_LOGIC_TRIBOOL_HPP #define BOOST_LOGIC_TRIBOOL_HPP #include #include #include #if BOOST_WORKAROUND(_MSC_VER, >= 1200) # pragma once #endif namespace boost { namespace logic { /// INTERNAL ONLY namespace detail { /** * INTERNAL ONLY * * \brief A type used only to uniquely identify the 'indeterminate' * function/keyword. */ struct indeterminate_t { #if BOOST_WORKAROUND(__BORLANDC__, < 0x0600) char dummy_; // BCB would use 8 bytes by default #endif }; } // end namespace detail /** * INTERNAL ONLY * The type of the 'indeterminate' keyword. This has the same type as the * function 'indeterminate' so that we can recognize when the keyword is * used. */ typedef bool (*indeterminate_keyword_t)(tribool, detail::indeterminate_t); /** * \brief Keyword and test function for the indeterminate tribool value * * The \c indeterminate function has a dual role. It's first role is * as a unary function that tells whether the tribool value is in the * "indeterminate" state. It's second role is as a keyword * representing the indeterminate (just like "true" and "false" * represent the true and false states). If you do not like the name * "indeterminate", and would prefer to use a different name, see the * macro \c BOOST_TRIBOOL_THIRD_STATE. * * \returns x.value == tribool::indeterminate_value * \throws nothrow */ inline bool indeterminate(tribool x, detail::indeterminate_t dummy = detail::indeterminate_t()); /** * \brief A 3-state boolean type. * * 3-state boolean values are either true, false, or * indeterminate. */ class tribool { private: /// INTERNAL ONLY struct dummy { void nonnull() {}; }; typedef void (dummy::*safe_bool)(); public: /** * Construct a new 3-state boolean value with the value 'false'. * * \throws nothrow */ tribool() : value(false_value) {} /** * Construct a new 3-state boolean value with the given boolean * value, which may be \c true or \c false. * * \throws nothrow */ tribool(bool value) : value(value? true_value : false_value) {} /** * Construct a new 3-state boolean value with an indeterminate value. * * \throws nothrow */ tribool(indeterminate_keyword_t) : value(indeterminate_value) {} /** * Use a 3-state boolean in a boolean context. Will evaluate true in a * boolean context only when the 3-state boolean is definitely true. * * \returns true if the 3-state boolean is true, false otherwise * \throws nothrow */ operator safe_bool() const { return value == true_value? &dummy::nonnull : 0; } /** * The actual stored value in this 3-state boolean, which may be false, true, * or indeterminate. */ enum value_t { false_value, true_value, indeterminate_value } value; }; // Check if the given tribool has an indeterminate value. Also doubles as a // keyword for the 'indeterminate' value inline bool indeterminate(tribool x, detail::indeterminate_t) { return x.value == tribool::indeterminate_value; } /** @defgroup logical Logical operations */ //@{ /** * \brief Computes the logical negation of a tribool * * \returns the logical negation of the tribool, according to the * table: * * * * * * * * * * * * * * * * *
!
*
false
true
true
false
indeterminate
indeterminate
* \throws nothrow */ inline tribool operator!(tribool x) { return x.value == tribool::false_value? tribool(true) :x.value == tribool::true_value? tribool(false) :tribool(indeterminate); } /** * \brief Computes the logical conjuction of two tribools * * \returns the result of logically ANDing the two tribool values, * according to the following table: * * * * * * * * * * * * * * * * * * * * * * * * * *
&&
false
true
indeterminate
false
false
false
false
true
false
true
indeterminate
indeterminate
false
indeterminate
indeterminate
* \throws nothrow */ inline tribool operator&&(tribool x, tribool y) { if (static_cast(!x) || static_cast(!y)) return false; else if (static_cast(x) && static_cast(y)) return true; else return indeterminate; } /** * \overload */ inline tribool operator&&(tribool x, bool y) { return y? x : tribool(false); } /** * \overload */ inline tribool operator&&(bool x, tribool y) { return x? y : tribool(false); } /** * \overload */ inline tribool operator&&(indeterminate_keyword_t, tribool x) { return !x? tribool(false) : tribool(indeterminate); } /** * \overload */ inline tribool operator&&(tribool x, indeterminate_keyword_t) { return !x? tribool(false) : tribool(indeterminate); } /** * \brief Computes the logical disjunction of two tribools * * \returns the result of logically ORing the two tribool values, * according to the following table: * * * * * * * * * * * * * * * * * * * * * * * * * *
||
false
true
indeterminate
false
false
true
indeterminate
true
true
true
true
indeterminate
indeterminate
true
indeterminate
* \throws nothrow */ inline tribool operator||(tribool x, tribool y) { if (static_cast(!x) && static_cast(!y)) return false; else if (static_cast(x) || static_cast(y)) return true; else return indeterminate; } /** * \overload */ inline tribool operator||(tribool x, bool y) { return y? tribool(true) : x; } /** * \overload */ inline tribool operator||(bool x, tribool y) { return x? tribool(true) : y; } /** * \overload */ inline tribool operator||(indeterminate_keyword_t, tribool x) { return x? tribool(true) : tribool(indeterminate); } /** * \overload */ inline tribool operator||(tribool x, indeterminate_keyword_t) { return x? tribool(true) : tribool(indeterminate); } //@} /** * \brief Compare tribools for equality * * \returns the result of comparing two tribool values, according to * the following table: * * * * * * * * * * * * * * * * * * * * * * * * * *
==
false
true
indeterminate
false
true
false
indeterminate
true
false
true
indeterminate
indeterminate
indeterminate
indeterminate
indeterminate
* \throws nothrow */ inline tribool operator==(tribool x, tribool y) { if (indeterminate(x) || indeterminate(y)) return indeterminate; else return x && y || !x && !y; } /** * \overload */ inline tribool operator==(tribool x, bool y) { return x == tribool(y); } /** * \overload */ inline tribool operator==(bool x, tribool y) { return tribool(x) == y; } /** * \overload */ inline tribool operator==(indeterminate_keyword_t, tribool x) { return tribool(indeterminate) == x; } /** * \overload */ inline tribool operator==(tribool x, indeterminate_keyword_t) { return tribool(indeterminate) == x; } /** * \brief Compare tribools for inequality * * \returns the result of comparing two tribool values for inequality, * according to the following table: * * * * * * * * * * * * * * * * * * * * * * * * * *
!=
false
true
indeterminate
false
false
true
indeterminate
true
true
false
indeterminate
indeterminate
indeterminate
indeterminate
indeterminate
* \throws nothrow */ inline tribool operator!=(tribool x, tribool y) { if (indeterminate(x) || indeterminate(y)) return indeterminate; else return !(x && y || !x && !y); } /** * \overload */ inline tribool operator!=(tribool x, bool y) { return x != tribool(y); } /** * \overload */ inline tribool operator!=(bool x, tribool y) { return tribool(x) != y; } /** * \overload */ inline tribool operator!=(indeterminate_keyword_t, tribool x) { return tribool(indeterminate) != x; } /** * \overload */ inline tribool operator!=(tribool x, indeterminate_keyword_t) { return x != tribool(indeterminate); } } } // end namespace boost::logic // Pull tribool and indeterminate into namespace "boost" namespace boost { using logic::tribool; using logic::indeterminate; } /** * \brief Declare a new name for the third state of a tribool * * Use this macro to declare a new name for the third state of a * tribool. This state can have any number of new names (in addition * to \c indeterminate), all of which will be equivalent. The new name will be * placed in the namespace in which the macro is expanded. * * Example: * BOOST_TRIBOOL_THIRD_STATE(true_or_false) * * tribool x(true_or_false); * // potentially set x * if (true_or_false(x)) { * // don't know what x is * } */ #define BOOST_TRIBOOL_THIRD_STATE(Name) \ inline bool \ Name(boost::logic::tribool x, \ boost::logic::detail::indeterminate_t dummy = \ boost::logic::detail::indeterminate_t()) \ { return x.value == boost::logic::tribool::indeterminate_value; } #endif // BOOST_LOGIC_TRIBOOL_HPP