filter_pattern.h

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#ifndef GRPPI_COMMON_FILTER_PATTERN_H
#define GRPPI_COMMON_FILTER_PATTERN_H

#include <type_traits>

namespace grppi {

template <typename Predicate>
class filter_t {
public:

  filter_t(Predicate && p) noexcept :
    predicate_{p}
  {}

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

private:
  Predicate predicate_;
};

namespace internal {

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

template<typename T>
struct is_filter<filter_t<T>> : std::true_type {};

} // namespace internal

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

template <typename T>
using requires_filter = typename std::enable_if_t<is_filter<T>, int>;

}

#endif