iteration_pattern.h

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#ifndef GRPPI_COMMON_ITERATION_PATTERN_H
#define GRPPI_COMMON_ITERATION_PATTERN_H

#include <type_traits>

namespace grppi {

template <typename Transformer, typename Predicate>
class iteration_t {
public:

  iteration_t(Transformer && t, Predicate && p) noexcept :
    transform_{t},
    predicate_{p}
  {}

  template <typename Item>
  bool predicate(Item && item) const {
    return predicate_(std::forward<Item>(item));
  }

  template <typename Item>
  auto transform(Item && item) const {
    return transform_(std::forward<Item>(item));
  }

  template<typename T>
  auto operator()(T && item){
    return transform(item);
  }

private:
  Transformer transform_;
  Predicate predicate_;
};

namespace internal {

template<typename T>
struct is_iteration : std::false_type {};

template<typename T, typename P>
struct is_iteration<iteration_t<T,P>> : std::true_type {};

} // namespace internal

template <typename T>
static constexpr bool is_iteration = internal::is_iteration<std::decay_t<T>>();

template <typename T>
using requires_iteration = typename std::enable_if_t<is_iteration<T>, int>;

}

#endif