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460 lines
12 KiB
460 lines
12 KiB
// 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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#if BOOST_WORKAROUND(_MSC_VER, >= 1200) |
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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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inline bool |
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indeterminate(tribool x, |
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detail::indeterminate_t dummy = detail::indeterminate_t()); |
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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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tribool() : 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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tribool(bool initial_value) : 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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tribool(indeterminate_keyword_t) : 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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operator safe_bool() const |
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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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inline bool indeterminate(tribool x, detail::indeterminate_t) |
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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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inline tribool operator!(tribool x) |
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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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inline tribool operator&&(tribool x, tribool y) |
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{ |
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if (static_cast<bool>(!x) || static_cast<bool>(!y)) |
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return false; |
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else if (static_cast<bool>(x) && static_cast<bool>(y)) |
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return true; |
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else |
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return indeterminate; |
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} |
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/** |
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* \overload |
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*/ |
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inline tribool operator&&(tribool x, bool y) |
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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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inline tribool operator&&(bool x, tribool y) |
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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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inline tribool operator&&(indeterminate_keyword_t, tribool x) |
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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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inline tribool operator&&(tribool x, indeterminate_keyword_t) |
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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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inline tribool operator||(tribool x, tribool y) |
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{ |
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if (static_cast<bool>(!x) && static_cast<bool>(!y)) |
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return false; |
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else if (static_cast<bool>(x) || static_cast<bool>(y)) |
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return true; |
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else |
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return indeterminate; |
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} |
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/** |
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* \overload |
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*/ |
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inline tribool operator||(tribool x, bool y) |
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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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inline tribool operator||(bool x, tribool y) |
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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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inline tribool operator||(indeterminate_keyword_t, tribool x) |
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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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inline tribool operator||(tribool x, indeterminate_keyword_t) |
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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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inline tribool operator==(tribool x, tribool y) |
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{ |
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if (indeterminate(x) || indeterminate(y)) |
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return indeterminate; |
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else |
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return (x && y) || (!x && !y); |
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} |
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/** |
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* \overload |
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*/ |
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inline tribool operator==(tribool x, bool y) { return x == tribool(y); } |
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/** |
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* \overload |
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*/ |
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inline tribool operator==(bool x, tribool y) { return tribool(x) == y; } |
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/** |
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* \overload |
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*/ |
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inline tribool operator==(indeterminate_keyword_t, tribool x) |
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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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inline tribool operator==(tribool x, indeterminate_keyword_t) |
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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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inline tribool operator!=(tribool x, tribool y) |
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{ |
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if (indeterminate(x) || indeterminate(y)) |
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return indeterminate; |
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else |
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return !((x && y) || (!x && !y)); |
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} |
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/** |
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* \overload |
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*/ |
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inline tribool operator!=(tribool x, bool y) { return x != tribool(y); } |
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/** |
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* \overload |
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*/ |
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inline tribool operator!=(bool x, tribool y) { return tribool(x) != y; } |
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/** |
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* \overload |
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*/ |
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inline tribool operator!=(indeterminate_keyword_t, tribool x) |
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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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inline tribool operator!=(tribool x, indeterminate_keyword_t) |
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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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