slice.hpp

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/*
 * Copyright (C) 1998-2018 ALPS Collaboration. See COPYRIGHT.TXT
 * All rights reserved. Use is subject to license terms. See LICENSE.TXT
 * For use in publications, see ACKNOWLEDGE.TXT
 */

/* $Id: obsvalue.h 3435 2009-11-28 14:45:38Z troyer $ */

#ifndef ALPS_TYPE_TRAITS_SLICE_HPP
#define ALPS_TYPE_TRAITS_SLICE_HPP

#include <alps/type_traits/is_sequence.hpp>
#include <alps/type_traits/element_type.hpp>

#include <type_traits>

namespace alps {

template <class T>
struct slice_index
{
  typedef std::size_t type;
};

template <class T>
typename std::enable_if<is_sequence<T>::value,
  std::pair<typename slice_index<T>::type,typename slice_index<T>::type >
>::type
slices (T const& x)
{
  return std::pair<typename slice_index<T>::type,typename slice_index<T>::type >(0,x.size());
}

template <class T>
typename std::enable_if<!is_sequence<T>::value,
  std::pair<typename slice_index<T>::type,typename slice_index<T>::type >
>::type
slices (T const&)
{
  return std::pair<typename slice_index<T>::type,typename slice_index<T>::type >(0,1);
}

template <class ValueType>
typename std::enable_if<is_sequence<ValueType>::value, std::string>::type
slice_name(ValueType const& ,unsigned i)
{
  return std::to_string(i);
}

template <class ValueType>
typename std::enable_if<!is_sequence<ValueType>::value, std::string>::type
slice_name(ValueType const& ,unsigned)
{
  return "";
}

template <class ValueType>
typename std::enable_if<is_sequence<ValueType>::value,
  typename element_type<ValueType>::type>::type
slice_value(ValueType const& x ,unsigned i)
{
  return i < x.size() ? x[i] : typename element_type<ValueType>::type();
}


template <class ValueType>
typename std::enable_if<!is_sequence<ValueType>::value, ValueType const&>::type
slice_value(ValueType const& x ,unsigned)
{
  return x;
}

template <class ValueType>
typename std::enable_if<is_sequence<ValueType>::value,
  typename element_type<ValueType>::type&>::type
slice_value(ValueType& x,unsigned i)
{
  return x[i];
}


template <class ValueType>
typename std::enable_if<!is_sequence<ValueType>::value, ValueType&>::type
slice_value(ValueType& x ,unsigned)
{
  return x;
}

template <class ValueType>
struct slice_it
{
  typedef typename element_type<ValueType>::type result_type;
  typedef ValueType const& first_argument_type;
  typedef typename slice_index<ValueType>::type second_argument_type;

  result_type operator()(ValueType const& x, second_argument_type i) const
  {
    return slice_value(x,i);
  }
};


} // end namespace alps

#endif // ALPS_TYPE_TRAITS_ELEMENT_TYPE_H