holds_alternative.hpp

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//
// Created by yonggyulee on 2/4/24.
//
 
#ifndef VCCC_VARIANTS_HOLDS_ALTERNATIVE_HPP
#define VCCC_VARIANTS_HOLDS_ALTERNATIVE_HPP
 
#include <type_traits>
 
#include "vccc/__utility/type_sequence.hpp"
#include "vccc/__variant/variant.hpp"
 
namespace vccc {
namespace detail {
 
template<typename T>
struct variant_holds_alternative_visitor {
  template<typename U, std::size_t I>
  constexpr bool operator()(const U&, in_place_index_t<I>) const {
    return I != variant_npos && std::is_same<T, U>::value;
  }
};
 
} // namespace detail
 
 
template<typename T, typename... Types, std::enable_if_t<
    (type_sequence<Types...>::template count<T> == 1)
, int> = 0>
constexpr bool holds_alternative(const variant<Types...>& v) noexcept {
  return detail::variant_raw_visit(v.index(), v._base().union_, detail::variant_holds_alternative_visitor<T>{});
}
 
 
} // namespace vccc
 
#endif // VCCC_VARIANTS_HOLDS_ALTERNATIVE_HPP