select.h

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// -*- C++ -*-

#if !defined(__ads_select_h__)
#define __ads_select_h__

#include "../defs.h"

#include <functional>

BEGIN_NAMESPACE_ADS

//-----------------------------------------------------------------------------
// @{

template<class Pair>
struct Select1st : 
  public std::unary_function<Pair, typename Pair::first_type> {
  typename Pair::first_type& 
  operator()(Pair& x) const {
    return x.first;
  }

  const typename Pair::first_type& 
  operator()(const Pair& x) const {
    return x.first;
  }
};

template<class Pair>
struct Select2nd : 
  public std::unary_function<Pair, typename Pair::second_type> {
  typename Pair::second_type& 
  operator()(Pair& x) const {
    return x.second;
  }

  const typename Pair::second_type& 
  operator()(const Pair& x) const {
    return x.second;
  }
};

template<class Pair>
inline
Select1st<Pair>
select_1st() {
  return Select1st<Pair>();
}

template<class Pair>
inline
Select2nd<Pair>
select_2nd() {
  return Select2nd<Pair>();
}



template<class Sequence, int N>
struct SelectElement : 
  public std::unary_function<Sequence, typename Sequence::value_type> {
  typedef std::unary_function<Sequence, typename Sequence::value_type>
  Base;
  typedef typename Base::argument_type argument_type;
  typedef typename Base::result_type result_type;

  result_type& 
  operator()(argument_type& x) const {
    return x[N];
  }

  const result_type& 
  operator()(const argument_type& x) const {
    return x[N];
  }
};

template<class Sequence, int N>
inline
SelectElement<Sequence,N>
select_element() {
  return SelectElement<Sequence,N>();
}

// @}

END_NAMESPACE_ADS

#endif

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