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