Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards



/* Copyright (c) 2002,2003 CrystalClear Software, Inc.
 * Use, modification and distribution is subject to the 
 * Boost Software License, Version 1.0. (See accompanying
 * file LICENSE_1_0.txt or
 * Author: Jeff Garland 
 * $Date: 2008-11-12 11:37:53 -0800 (Wed, 12 Nov 2008) $

#include <exception>
#include <stdexcept>
#include <boost/config.hpp>
#include <boost/throw_exception.hpp>
#include <boost/mpl/if.hpp>
#include <boost/type_traits/is_base_of.hpp>

namespace boost {

//! Namespace containing constrained_value template and types
namespace CV {
  //! Represent a min or max violation type
  enum violation_enum {min_violation, max_violation};
  //! A template to specify a constrained basic value type
  /*! This template provides a quick way to generate
   *  an integer type with a constrained range.  The type
   *  provides for the ability to specify the min, max, and
   *  and error handling policy.
   *  <b>value policies</b>
   *  A class that provides the range limits via the min and
   *  max functions as well as a function on_error that 
   *  determines how errors are handled.  A common strategy
   *  would be to assert or throw and exception.  The on_error
   *  is passed both the current value and the new value that
   *  is in error.
  template<class value_policies>
  class constrained_value {
    typedef typename value_policies::value_type value_type;
    //    typedef except_type exception_type;
    constrained_value(value_type value) : value_((min)())
    constrained_value& operator=(value_type v)
      return *this;
    //! Return the max allowed value (traits method)
    static value_type max BOOST_PREVENT_MACRO_SUBSTITUTION () {return (value_policies::max)();}
    //! Return the min allowed value (traits method)
    static value_type min BOOST_PREVENT_MACRO_SUBSTITUTION () {return (value_policies::min)();}
    //! Coerce into the representation type
    operator value_type() const {return value_;}
    value_type value_;
    void assign(value_type value)
      //adding 1 below gets rid of a compiler warning which occurs when the 
      //min_value is 0 and the type is unsigned....
      if (value+1 < (min)()+1) {
        value_policies::on_error(value_, value, min_violation);
      if (value > (max)()) {
        value_policies::on_error(value_, value, max_violation);
      value_ = value;

  //! Template to shortcut the constrained_value policy creation process
  template<typename rep_type, rep_type min_value, 
           rep_type max_value, class exception_type>
  class simple_exception_policy
    struct exception_wrapper : public exception_type
      // In order to support throw_exception mechanism in the BOOST_NO_EXCEPTIONS mode,
      // we'll have to provide a way to acquire std::exception from the exception being thrown.
      // However, we cannot derive from it, since it would make it interceptable by this class,
      // which might not be what the user wanted.
      operator std::out_of_range () const
        // TODO: Make the message more descriptive by using arguments to on_error
        return std::out_of_range("constrained value boundary has been violated");

    typedef typename mpl::if_<
      is_base_of< std::exception, exception_type >,
    >::type actual_exception_type;

    typedef rep_type value_type;
    static rep_type min BOOST_PREVENT_MACRO_SUBSTITUTION () { return min_value; }
    static rep_type max BOOST_PREVENT_MACRO_SUBSTITUTION () { return max_value; }
    static void on_error(rep_type, rep_type, violation_enum)

} } //namespace CV