source: lemon-0.x/lemon/utility.h @ 1435:8e85e6bbefdf

/* -*- C++ -*-
 * lemon/utility.h - Part of LEMON, a generic C++ optimization library
 *
 * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi
 * Kutatocsoport (Egervary Research Group on Combinatorial Optimization,
 * EGRES).
 *
 * Permission to use, modify and distribute this software is granted
 * provided that this copyright notice appears in all copies. For
 * precise terms see the accompanying LICENSE file.
 *
 * This software is provided "AS IS" with no warranty of any kind,
 * express or implied, and with no claim as to its suitability for any
 * purpose.
 *
 * This file contains a modified version of the enable_if library from BOOST.
 * See the appropriate copyright notice below.
 */

// Boost enable_if library

// Copyright 2003 © The Trustees of Indiana University.

// Use, modification, and distribution is subject to the Boost Software
// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

//    Authors: Jaakko Järvi (jajarvi at osl.iu.edu)
//             Jeremiah Willcock (jewillco at osl.iu.edu)
//             Andrew Lumsdaine (lums at osl.iu.edu)


#ifndef LEMON_UTILITY_H
#define LEMON_UTILITY_H

namespace lemon
{

  /// Basic type for defining "tags". A "YES" condition for enable_if.

  /// \todo This should go to a separate "basic_types.h" (or something)
  /// file.
  struct True {
    static const bool value = true;
  };

  /// Basic type for defining "tags". A "NO" condition for enable_if.
  struct False {
    static const bool value = false;
  };

  template <typename T>
  struct Wrap {
    const T &value;
    Wrap(const T &t) : value(t) {}
  };

  /**************** dummy class to avoid ambiguity ****************/

  template<int T> struct dummy { dummy(int) {} };

  /**************** enable_if from BOOST ****************/
 
  template <bool B, class T = void>
  struct enable_if_c {
    typedef T type;
  };

  template <class T>
  struct enable_if_c<false, T> {};

  template <class Cond, class T = void> 
  struct enable_if : public enable_if_c<Cond::value, T> {};

  template <bool B, class T>
  struct lazy_enable_if_c {
    typedef typename T::type type;
  };

  template <class T>
  struct lazy_enable_if_c<false, T> {};

  template <class Cond, class T> 
  struct lazy_enable_if : public lazy_enable_if_c<Cond::value, T> {};


  template <bool B, class T = void>
  struct disable_if_c {
    typedef T type;
  };

  template <class T>
  struct disable_if_c<true, T> {};

  template <class Cond, class T = void> 
  struct disable_if : public disable_if_c<Cond::value, T> {};

  template <bool B, class T>
  struct lazy_disable_if_c {
    typedef typename T::type type;
  };

  template <class T>
  struct lazy_disable_if_c<true, T> {};

  template <class Cond, class T> 
  struct lazy_disable_if : public lazy_disable_if_c<Cond::value, T> {};

  // smart referencing

  template <typename _Type, typename Enable = void>
  struct SmartReference {
    typedef _Type& Type;
  };
  
  template <typename _Type>
  struct SmartReference<
    _Type, 
    typename enable_if<typename _Type::NeedCopy, void>::type
  > {
    typedef _Type Type;
  };

  template <typename _Type, typename Enable = void>
  struct SmartConstReference {
    typedef const _Type& Type;
  };
  
  template <typename _Type>
  struct SmartConstReference<
    _Type, 
    typename enable_if<typename _Type::NeedCopy, void>::type
  > {
    typedef const _Type Type;
  };

  template <typename _Type, typename Enable = void>
  struct SmartParameter {
    typedef _Type& Type;
  };
  
  template <typename _Type>
  struct SmartParameter<
    _Type, 
    typename enable_if<typename _Type::NeedCopy, void>::type
  > {
    typedef const _Type& Type;
  };

} // namespace lemon

#endif