lemon/bits/enable_if.h
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     1 /* -*- mode: C++; indent-tabs-mode: nil; -*-
       
     2  *
       
     3  * This file is a part of LEMON, a generic C++ optimization library.
       
     4  *
       
     5  * Copyright (C) 2003-2008
       
     6  * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
       
     7  * (Egervary Research Group on Combinatorial Optimization, EGRES).
       
     8  *
       
     9  * Permission to use, modify and distribute this software is granted
       
    10  * provided that this copyright notice appears in all copies. For
       
    11  * precise terms see the accompanying LICENSE file.
       
    12  *
       
    13  * This software is provided "AS IS" with no warranty of any kind,
       
    14  * express or implied, and with no claim as to its suitability for any
       
    15  * purpose.
       
    16  *
       
    17  */
       
    18 
       
    19 // This file contains a modified version of the enable_if library from BOOST.
       
    20 // See the appropriate copyright notice below.
       
    21 
       
    22 // Boost enable_if library
       
    23 
       
    24 // Copyright 2003 (c) The Trustees of Indiana University.
       
    25 
       
    26 // Use, modification, and distribution is subject to the Boost Software
       
    27 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
       
    28 // http://www.boost.org/LICENSE_1_0.txt)
       
    29 
       
    30 //    Authors: Jaakko Jarvi (jajarvi at osl.iu.edu)
       
    31 //             Jeremiah Willcock (jewillco at osl.iu.edu)
       
    32 //             Andrew Lumsdaine (lums at osl.iu.edu)
       
    33 
       
    34 
       
    35 #ifndef LEMON_BITS_ENABLE_IF_H
       
    36 #define LEMON_BITS_ENABLE_IF_H
       
    37 
       
    38 ///\file
       
    39 ///\brief Miscellaneous basic utilities
       
    40 
       
    41 namespace lemon
       
    42 {
       
    43 
       
    44   /// Basic type for defining "tags". A "YES" condition for \c enable_if.
       
    45 
       
    46   /// Basic type for defining "tags". A "YES" condition for \c enable_if.
       
    47   ///
       
    48   ///\sa False
       
    49   struct True {
       
    50     ///\e
       
    51     static const bool value = true;
       
    52   };
       
    53 
       
    54   /// Basic type for defining "tags". A "NO" condition for \c enable_if.
       
    55 
       
    56   /// Basic type for defining "tags". A "NO" condition for \c enable_if.
       
    57   ///
       
    58   ///\sa True
       
    59   struct False {
       
    60     ///\e
       
    61     static const bool value = false;
       
    62   };
       
    63 
       
    64 
       
    65 
       
    66   template <typename T>
       
    67   struct Wrap {
       
    68     const T &value;
       
    69     Wrap(const T &t) : value(t) {}
       
    70   };
       
    71 
       
    72   /**************** dummy class to avoid ambiguity ****************/
       
    73 
       
    74   template<int T> struct dummy { dummy(int) {} };
       
    75 
       
    76   /**************** enable_if from BOOST ****************/
       
    77 
       
    78   template <typename Type, typename T = void>
       
    79   struct exists {
       
    80     typedef T type;
       
    81   };
       
    82 
       
    83 
       
    84   template <bool B, class T = void>
       
    85   struct enable_if_c {
       
    86     typedef T type;
       
    87   };
       
    88 
       
    89   template <class T>
       
    90   struct enable_if_c<false, T> {};
       
    91 
       
    92   template <class Cond, class T = void>
       
    93   struct enable_if : public enable_if_c<Cond::value, T> {};
       
    94 
       
    95   template <bool B, class T>
       
    96   struct lazy_enable_if_c {
       
    97     typedef typename T::type type;
       
    98   };
       
    99 
       
   100   template <class T>
       
   101   struct lazy_enable_if_c<false, T> {};
       
   102 
       
   103   template <class Cond, class T>
       
   104   struct lazy_enable_if : public lazy_enable_if_c<Cond::value, T> {};
       
   105 
       
   106 
       
   107   template <bool B, class T = void>
       
   108   struct disable_if_c {
       
   109     typedef T type;
       
   110   };
       
   111 
       
   112   template <class T>
       
   113   struct disable_if_c<true, T> {};
       
   114 
       
   115   template <class Cond, class T = void>
       
   116   struct disable_if : public disable_if_c<Cond::value, T> {};
       
   117 
       
   118   template <bool B, class T>
       
   119   struct lazy_disable_if_c {
       
   120     typedef typename T::type type;
       
   121   };
       
   122 
       
   123   template <class T>
       
   124   struct lazy_disable_if_c<true, T> {};
       
   125 
       
   126   template <class Cond, class T>
       
   127   struct lazy_disable_if : public lazy_disable_if_c<Cond::value, T> {};
       
   128 
       
   129 } // namespace lemon
       
   130 
       
   131 #endif