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  1. #ifndef CONSTRAINED_VALUE_HPP___
  2. #define CONSTRAINED_VALUE_HPP___
  3.  
  4. /* Copyright (c) 2002,2003 CrystalClear Software, Inc.
  5.  * Use, modification and distribution is subject to the
  6.  * Boost Software License, Version 1.0. (See accompanying
  7.  * file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
  8.  * Author: Jeff Garland
  9.  * $Date$
  10.  */
  11.  
  12. #include <exception>
  13. #include <stdexcept>
  14. #include <boost/config.hpp>
  15. #include <boost/throw_exception.hpp>
  16. #include <boost/mpl/if.hpp>
  17. #include <boost/type_traits/is_base_of.hpp>
  18.  
  19. namespace mars_boost {} namespace boost = mars_boost; namespace mars_boost {
  20.  
  21. //! Namespace containing constrained_value template and types
  22. namespace CV {
  23.   //! Represent a min or max violation type
  24.   enum violation_enum {min_violation, max_violation};
  25.  
  26.   //! A template to specify a constrained basic value type
  27.   /*! This template provides a quick way to generate
  28.    *  an integer type with a constrained range.  The type
  29.    *  provides for the ability to specify the min, max, and
  30.    *  and error handling policy.
  31.    *  
  32.    *  <b>value policies</b>
  33.    *  A class that provides the range limits via the min and
  34.    *  max functions as well as a function on_error that
  35.    *  determines how errors are handled.  A common strategy
  36.    *  would be to assert or throw and exception.  The on_error
  37.    *  is passed both the current value and the new value that
  38.    *  is in error.
  39.    *
  40.    */
  41.   template<class value_policies>
  42.   class constrained_value {
  43.   public:
  44.     typedef typename value_policies::value_type value_type;
  45.     //    typedef except_type exception_type;
  46.     constrained_value(value_type value) : value_((min)())
  47.     {
  48.       assign(value);
  49.     }
  50.     constrained_value& operator=(value_type v)
  51.     {
  52.       assign(v);
  53.       return *this;
  54.     }
  55.     //! Return the max allowed value (traits method)
  56.     static value_type max BOOST_PREVENT_MACRO_SUBSTITUTION () {return (value_policies::max)();}
  57.     //! Return the min allowed value (traits method)
  58.     static value_type min BOOST_PREVENT_MACRO_SUBSTITUTION () {return (value_policies::min)();}
  59.     //! Coerce into the representation type
  60.     operator value_type() const {return value_;}
  61.   protected:
  62.     value_type value_;
  63.   private:
  64.     void assign(value_type value)
  65.     {
  66.       //adding 1 below gets rid of a compiler warning which occurs when the
  67.       //min_value is 0 and the type is unsigned....
  68.       if (value+1 < (min)()+1) {
  69.         value_policies::on_error(value_, value, min_violation);
  70.         return;
  71.       }
  72.       if (value > (max)()) {
  73.         value_policies::on_error(value_, value, max_violation);
  74.         return;
  75.       }
  76.       value_ = value;
  77.     }
  78. };
  79.  
  80.   //! Template to shortcut the constrained_value policy creation process
  81.   template<typename rep_type, rep_type min_value,
  82.            rep_type max_value, class exception_type>
  83.   class simple_exception_policy
  84.   {
  85.     struct exception_wrapper : public exception_type
  86.     {
  87.       // In order to support throw_exception mechanism in the BOOST_NO_EXCEPTIONS mode,
  88.       // we'll have to provide a way to acquire std::exception from the exception being thrown.
  89.       // However, we cannot derive from it, since it would make it interceptable by this class,
  90.       // which might not be what the user wanted.
  91.       operator std::out_of_range () const
  92.       {
  93.         // TODO: Make the message more descriptive by using arguments to on_error
  94.         return std::out_of_range("constrained value boundary has been violated");
  95.       }
  96.     };
  97.  
  98.     typedef typename mpl::if_<
  99.       is_base_of< std::exception, exception_type >,
  100.       exception_type,
  101.       exception_wrapper
  102.     >::type actual_exception_type;
  103.  
  104.   public:
  105.     typedef rep_type value_type;
  106.     static rep_type min BOOST_PREVENT_MACRO_SUBSTITUTION () { return min_value; }
  107.     static rep_type max BOOST_PREVENT_MACRO_SUBSTITUTION () { return max_value; }
  108.     static void on_error(rep_type, rep_type, violation_enum)
  109.     {
  110.       mars_boost::throw_exception(actual_exception_type());
  111.     }
  112.   };
  113.  
  114.  
  115.  
  116. } } //namespace CV
  117.  
  118.  
  119.  
  120.  
  121. #endif
  122.  
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