farm_pattern.h

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#ifndef GRPPI_COMMON_FARM_PATTERN_H
#define GRPPI_COMMON_FARM_PATTERN_H

#include <type_traits>

namespace grppi {

template <typename Transformer>
class farm_t {
public:

  using transformer_type = Transformer;

  farm_t(int n, Transformer && t) noexcept :
    cardinality_{n}, transformer_{t}
  {}

  int cardinality() const noexcept {
    return cardinality_;
  }

  Transformer & transformer(){
    return transformer_;
  }
  template <typename I>
  auto operator()(I && item) const {
    return transformer_(std::forward<I>(item));
  }

private:
  int cardinality_;
  Transformer transformer_;
};

namespace internal {

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

template<typename T>
struct is_farm<farm_t<T>> : std::true_type {};

} // namespace internal

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

template <typename T>
using requires_farm = typename std::enable_if_t<is_farm<T>, int>;

}

#endif