iterator_traits.h

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#ifndef GRPPI_COMMON_ITERATOR_TRAITS_H
#define GRPPI_COMMON_ITERATOR_TRAITS_H

namespace grppi{

namespace internal {

template<typename T, typename = void>
struct is_iterator
{
  static constexpr bool value = false;
};

template<typename T>
struct is_iterator<T, typename std::enable_if<!std::is_same<typename std::iterator_traits<T>::value_type, void>::value>::type>
{
  static constexpr bool value = true;
};

template<typename T, typename ...other_T>
struct are_iterators
{
  static constexpr bool value = is_iterator<T>::value && are_iterators<other_T...>::value;
};

template<typename T>
struct are_iterators<T>
{
  static constexpr bool value = is_iterator<T>::value;
};

}

template <typename T>
constexpr bool is_iterator = internal::is_iterator<T>::value;

template <typename T>
using requires_iterator = std::enable_if_t<is_iterator<T>, int>;

template<typename ...T>
constexpr bool are_iterators = internal::are_iterators<T...>::value;

template<typename ...T>
using requires_iterators = std::enable_if_t<are_iterators<T...>, int>;

}

#endif