28925996281

Committed 08 Jul 2026 07:39AM UTC coverage: 99.833% (-0.1%) from 99.939%

Build # 28925996281

Build Type

push

github

Committed by

web-flow

Commit Message

Fix brace initialization of empty collection nodes (issue #502) (#524)

* Fix brace initialization of empty collection nodes

Preserve the type of empty mapping and sequence nodes when they are passed
through brace initialization, e.g. node{node::mapping()}.

Previously this form selected the initializer-list constructor and treated the
single empty mapping node as a sequence element. Track whether initializer-list
entries were created directly from a basic_node and unwrap the narrow empty
collection case without changing existing scalar initializer-list behavior.

Add regression coverage for empty mapping/sequence brace initialization and keep
single scalar brace initialization as a one-element sequence.

* Fix node_ref_storage conversion for initializer-list nodes

Allow node_ref_storage to be implicitly constructed from basic_node lvalues and
rvalues so initializer_list elements preserve the direct-node marker across
compilers.

This keeps node{node::mapping()} and node{node::sequence()} on the intended
empty collection unwrap path instead of falling through to the generic variadic
constructor.

* Keep explicit node_ref_storage constructors

Restore explicit on the direct basic_node node_ref_storage constructors and
handle the initializer-list empty collection case through the variadic
constructor path instead.

GCC/Clang select the variadic constructor when creating initializer_list
elements for node{node::mapping()} and node{node::sequence()}. Mark that
storage as a direct node only when it receives exactly one basic_node argument,
so the initializer-list constructor can preserve empty collection nodes without
allowing broader implicit conversions.

Update the constructor documentation and add coverage for duplicate-anchor
destruction.

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12 of 12 new or added lines in 2 files covered. (100.0%)

1 existing line in 1 file now uncovered.

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99.09

/include/fkYAML/node.hpp

//  _______   __ __   __  _____   __  __  __
// |   __| |_/  |  \_/  |/  _  \ /  \/  \|  |     fkYAML: A C++ header-only YAML library
// |   __|  _  < \_   _/|  ___  |    _   |  |___  version 0.4.2
// |__|  |_| \__|  |_|  |_|   |_|___||___|______| https://github.com/fktn-k/fkYAML
//
// SPDX-FileCopyrightText: 2023-2025 Kensuke Fukutani <fktn.dev@gmail.com>
// SPDX-License-Identifier: MIT

#ifndef FK_YAML_NODE_HPP
#define FK_YAML_NODE_HPP

#include <algorithm>
#include <cstdint>
#include <cstring>
#include <initializer_list>
#include <map>
#include <memory>
#include <string>
#include <type_traits>
#include <vector>

#include <fkYAML/detail/macros/define_macros.hpp>
#include <fkYAML/detail/assert.hpp>
#include <fkYAML/detail/document_metainfo.hpp>
#include <fkYAML/detail/exception_safe_allocation.hpp>
#include <fkYAML/detail/input/deserializer.hpp>
#include <fkYAML/detail/input/input_adapter.hpp>
#include <fkYAML/detail/iterator.hpp>
#include <fkYAML/detail/map_range_proxy.hpp>
#include <fkYAML/detail/meta/node_traits.hpp>
#include <fkYAML/detail/meta/stl_supplement.hpp>
#include <fkYAML/detail/meta/type_traits.hpp>
#include <fkYAML/detail/node_attrs.hpp>
#include <fkYAML/detail/node_property.hpp>
#include <fkYAML/detail/node_ref_storage.hpp>
#include <fkYAML/detail/output/serializer.hpp>
#include <fkYAML/detail/reverse_iterator.hpp>
#include <fkYAML/detail/types/node_t.hpp>
#include <fkYAML/detail/types/yaml_version_t.hpp>
#include <fkYAML/exception.hpp>
#include <fkYAML/node_type.hpp>
#include <fkYAML/node_value_converter.hpp>
#include <fkYAML/ordered_map.hpp>

FK_YAML_NAMESPACE_BEGIN

/// @brief A class to store value of YAML nodes.
/// @sa https://fktn-k.github.io/fkYAML/api/basic_node/
template <
    template <typename, typename...> class SequenceType, template <typename, typename, typename...> class MappingType,
    typename BooleanType, typename IntegerType, typename FloatNumberType, typename StringType,
    template <typename, typename = void> class ConverterType>
class basic_node {
public:
    /// @brief A type for sequence basic_node values.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/sequence_type/
    using sequence_type = SequenceType<basic_node, std::allocator<basic_node>>;

    /// @brief A type for mapping basic_node values.
    /// @note std::unordered_map is not supported since it does not allow incomplete types.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/mapping_type/
    using mapping_type = MappingType<basic_node, basic_node>;

    /// @brief A type for boolean basic_node values.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/boolean_type/
    using boolean_type = BooleanType;

    /// @brief A type for integer basic_node values.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/integer_type/
    using integer_type = IntegerType;

    /// @brief A type for float number basic_node values.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/float_number_type/
    using float_number_type = FloatNumberType;

    /// @brief A type for string basic_node values.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/string_type/
    using string_type = StringType;

    /// @brief A type of elements in a basic_node container.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/#container-types
    using value_type = basic_node;

    /// @brief A type of reference to a basic_node element.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/#container-types
    using reference = value_type&;

    /// @brief A type of constant reference to a basic_node element.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/#container-types
    using const_reference = const value_type&;

    /// @brief A type of a pointer to a basic_node element.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/#container-types
    using pointer = value_type*;

    /// @brief A type of a constant pointer to a basic_node element.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/#container-types
    using const_pointer = const value_type*;

    /// @brief A type to represent basic_node container sizes.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/#container-types
    using size_type = std::size_t;

    /// @brief A type to represent differences between basic_node iterators.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/#container-types
    using difference_type = std::ptrdiff_t;

    /// @brief A type for iterators of basic_node containers.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/iterator/
    using iterator = fkyaml::detail::iterator<basic_node>;

    /// @brief A type for constant iterators of basic_node containers.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/iterator/
    using const_iterator = fkyaml::detail::iterator<const basic_node>;

    /// @brief A type for reverse iterators of basic_node containers.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/reverse_iterator/
    using reverse_iterator = fkyaml::detail::reverse_iterator<iterator>;

    /// @brief A type for constant reverse iterators of basic_node containers.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/reverse_iterator/
    using const_reverse_iterator = fkyaml::detail::reverse_iterator<const_iterator>;

    /// @brief A helper alias to determine converter type for the given target native data type.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/value_converter_type/
    template <typename T, typename SFINAE>
    using value_converter_type = ConverterType<T, SFINAE>;

    /// @brief Definition of node value types.
    /// @deprecated Use fkyaml::node_type enum class. (since 0.3.12)
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/node_t/
    using node_t = detail::node_t;

    /// @brief Definition of YAML version types.
    /// @deprecated Use fkyaml::yaml_version_type enum class. (since 0.3.12)
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/yaml_version_t/
    using yaml_version_t = detail::yaml_version_t;

    /// @brief A type for mapping range objects for the map_items() function.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/map_range/
    using map_range = fkyaml::detail::map_range_proxy<basic_node>;

    /// @brief A type for constant mapping range objects for the map_items() function.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/map_range/
    using const_map_range = fkyaml::detail::map_range_proxy<const basic_node>;

private:
    template <typename BasicNodeType>
    friend struct fkyaml::detail::external_node_constructor;

    template <typename BasicNodeType>
    friend class fkyaml::detail::basic_deserializer;

    template <typename BasicNodeType>
    friend class fkyaml::detail::basic_serializer;

    /// @brief A type for YAML docs deserializers.
    using deserializer_type = detail::basic_deserializer<basic_node>;
    /// @brief A type for YAML docs serializers.
    using serializer_type = detail::basic_serializer<basic_node>;
    /// @brief A helper type alias for std::initializer_list.
    using initializer_list_t = std::initializer_list<detail::node_ref_storage<basic_node>>;

    /// @brief The actual storage for a YAML node value of the @ref basic_node class.
    /// @details This union combines the different storage types for the YAML value types defined in @ref node_t.
    /// @note Container types are stored as pointers so that the size of this union will not exceed 64 bits by
    /// default.
    union node_value {
        /// @brief Constructs a new basic_node Value object for null types.
        node_value() = default;

        /// @brief Constructs a new basic_node value object with a node type. The default value for the specified
        /// type will be assigned.
        /// @param[in] type A node type.
        explicit node_value(detail::node_attr_t value_type_bit) {
            switch (value_type_bit) {
            case detail::node_attr_bits::seq_bit:
                p_seq = detail::create_object<sequence_type>();
                break;
            case detail::node_attr_bits::map_bit:
                p_map = detail::create_object<mapping_type>();
                break;
            case detail::node_attr_bits::null_bit:
                p_map = nullptr;
                break;
            case detail::node_attr_bits::bool_bit:
                boolean = static_cast<boolean_type>(false);
                break;
            case detail::node_attr_bits::int_bit:
                integer = static_cast<integer_type>(0);
                break;
            case detail::node_attr_bits::float_bit:
                float_val = static_cast<float_number_type>(0.0);
                break;
            case detail::node_attr_bits::string_bit:
                p_str = detail::create_object<string_type>();
                break;
            default:                   // LCOV_EXCL_LINE
                detail::unreachable(); // LCOV_EXCL_LINE
            }
        }

        /// @brief Destroys the existing Node value. This process is recursive if the specified node type is for
        /// containers.
        /// @param[in] type A Node type to determine the value to be destroyed.
        void destroy(detail::node_attr_t value_type_bit) {
            switch (value_type_bit) {
            case detail::node_attr_bits::seq_bit:
                p_seq->clear();
                detail::destroy_object<sequence_type>(p_seq);
                p_seq = nullptr;
                break;
            case detail::node_attr_bits::map_bit:
                p_map->clear();
                detail::destroy_object<mapping_type>(p_map);
                p_map = nullptr;
                break;
            case detail::node_attr_bits::string_bit:
                detail::destroy_object<string_type>(p_str);
                p_str = nullptr;
                break;
            default:
                break;
            }
        }

        /// A pointer to the value of sequence type.
        sequence_type* p_seq;
        /// A pointer to the value of mapping type. This pointer is also used when node type is null.
        mapping_type* p_map {nullptr};
        /// A value of boolean type.
        boolean_type boolean;
        /// A value of integer type.
        integer_type integer;
        /// A value of float number type.
        float_number_type float_val;
        /// A pointer to the value of string type.
        string_type* p_str;
    };

public:
    /// @brief Constructs a new basic_node object of null type.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/constructor/
    basic_node() = default;

    /// @brief Constructs a new basic_node object with a specified type.
    /// @param[in] type A YAML node type.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/constructor/
    FK_YAML_DEPRECATED("Since 0.3.12; Use explicit basic_node(const node_type)")
    explicit basic_node(const node_t type)
        : basic_node(detail::convert_to_node_type(type)) {
    }

    explicit basic_node(const node_type type)
        : m_attrs(detail::node_attr_bits::from_node_type(type)),
          m_value(m_attrs & detail::node_attr_mask::value) {
    }

    /// @brief Copy constructor of the basic_node class.
    /// @param[in] rhs A basic_node object to be copied with.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/constructor/
    basic_node(const basic_node& rhs)
        : m_attrs(rhs.m_attrs),
          mp_meta(rhs.mp_meta),
          m_prop(rhs.m_prop) {
        if FK_YAML_LIKELY (!has_anchor_name()) {
            switch (m_attrs & detail::node_attr_mask::value) {
            case detail::node_attr_bits::seq_bit:
                m_value.p_seq = detail::create_object<sequence_type>(*(rhs.m_value.p_seq));
                break;
            case detail::node_attr_bits::map_bit:
                m_value.p_map = detail::create_object<mapping_type>(*(rhs.m_value.p_map));
                break;
            case detail::node_attr_bits::null_bit:
                m_value.p_map = nullptr;
                break;
            case detail::node_attr_bits::bool_bit:
                m_value.boolean = rhs.m_value.boolean;
                break;
            case detail::node_attr_bits::int_bit:
                m_value.integer = rhs.m_value.integer;
                break;
            case detail::node_attr_bits::float_bit:
                m_value.float_val = rhs.m_value.float_val;
                break;
            case detail::node_attr_bits::string_bit:
                m_value.p_str = detail::create_object<string_type>(*(rhs.m_value.p_str));
                break;
            default:                   // LCOV_EXCL_LINE
                detail::unreachable(); // LCOV_EXCL_LINE
            }
        }
    }

    /// @brief Move constructor of the basic_node class.
    /// @param[in] rhs A basic_node object to be moved from.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/constructor/
    basic_node(basic_node&& rhs) noexcept
        : m_attrs(rhs.m_attrs),
          mp_meta(std::move(rhs.mp_meta)),
          m_prop(std::move(rhs.m_prop)) {
        if FK_YAML_LIKELY (!has_anchor_name()) {
            switch (m_attrs & detail::node_attr_mask::value) {
            case detail::node_attr_bits::seq_bit:
                FK_YAML_ASSERT(rhs.m_value.p_seq != nullptr);
                m_value.p_seq = rhs.m_value.p_seq;
                rhs.m_value.p_seq = nullptr;
                break;
            case detail::node_attr_bits::map_bit:
                FK_YAML_ASSERT(rhs.m_value.p_map != nullptr);
                m_value.p_map = rhs.m_value.p_map;
                rhs.m_value.p_map = nullptr;
                break;
            case detail::node_attr_bits::null_bit:
                FK_YAML_ASSERT(rhs.m_value.p_map == nullptr);
                m_value.p_map = rhs.m_value.p_map;
                break;
            case detail::node_attr_bits::bool_bit:
                m_value.boolean = rhs.m_value.boolean;
                rhs.m_value.boolean = static_cast<boolean_type>(false);
                break;
            case detail::node_attr_bits::int_bit:
                m_value.integer = rhs.m_value.integer;
                rhs.m_value.integer = static_cast<integer_type>(0);
                break;
            case detail::node_attr_bits::float_bit:
                m_value.float_val = rhs.m_value.float_val;
                rhs.m_value.float_val = static_cast<float_number_type>(0.0);
                break;
            case detail::node_attr_bits::string_bit:
                FK_YAML_ASSERT(rhs.m_value.p_str != nullptr);
                m_value.p_str = rhs.m_value.p_str;
                rhs.m_value.p_str = nullptr;
                break;
            default:                   // LCOV_EXCL_LINE
                detail::unreachable(); // LCOV_EXCL_LINE
            }
        }

        rhs.m_attrs = detail::node_attr_bits::default_bits;
        rhs.m_value.p_map = nullptr;
    }

    /// @brief Construct a new basic_node object from a value of compatible types.
    /// @tparam CompatibleType Type of native data which is compatible with node values.
    /// @tparam U Type of compatible native data without cv-qualifiers and reference.
    /// @param[in] val The value of a compatible type.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/constructor/
    template <
        typename CompatibleType, typename U = detail::remove_cvref_t<CompatibleType>,
        detail::enable_if_t<
            detail::conjunction<
                detail::negation<detail::is_basic_node<U>>,
                detail::disjunction<detail::is_node_compatible_type<basic_node, U>>>::value,
            int> = 0>
    basic_node(CompatibleType&& val) noexcept(
        noexcept(ConverterType<U, void>::to_node(std::declval<basic_node&>(), std::declval<CompatibleType>()))) {
        ConverterType<U, void>::to_node(*this, std::forward<CompatibleType>(val));
    }

    /// @brief Construct a new basic node object with a node_ref_storage object.
    /// @tparam NodeRefStorageType Type of basic_node with reference.
    /// @param[in] node_ref_storage A node_ref_storage template class object.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/constructor/
    template <
        typename NodeRefStorageType,
        detail::enable_if_t<detail::is_node_ref_storage<NodeRefStorageType>::value, int> = 0>
    basic_node(const NodeRefStorageType& node_ref_storage) noexcept
        : basic_node(node_ref_storage.release()) {
    }

    /// @brief Construct a new basic node object with std::initializer_list.
    /// @param[in] init A initializer list of basic_node objects.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/constructor/
    basic_node(initializer_list_t init) {
        if (init.size() == 1 && init.begin()->has_node_ref()) {
            const auto& node_ref = *init.begin();
            if ((node_ref->is_sequence() || node_ref->is_mapping()) && node_ref->empty() && !node_ref->is_anchor() &&
                !node_ref->has_tag_name()) {
                basic_node(node_ref.release()).swap(*this);
                return;
            }
        }

        bool is_mapping =
            std::all_of(init.begin(), init.end(), [](const detail::node_ref_storage<basic_node>& node_ref) {
                // Do not use is_sequence_impl() since node_ref may be an anchor or alias.
                return node_ref->is_sequence() && node_ref->size() == 2;
            });

        if (is_mapping) {
            m_attrs = detail::node_attr_bits::map_bit;
            m_value.p_map = detail::create_object<mapping_type>();

            auto& map = *m_value.p_map;
            for (auto& elem_ref : init) {
                auto elem = elem_ref.release();
                auto& seq = *elem.m_value.p_seq;
                map.emplace(std::move(seq[0]), std::move(seq[1]));
            }
        }
        else {
            m_attrs = detail::node_attr_bits::seq_bit;
            m_value.p_seq = detail::create_object<sequence_type>();

            auto& seq = *m_value.p_seq;
            seq.reserve(std::distance(init.begin(), init.end()));
            for (auto& elem_ref : init) {
                seq.emplace_back(std::move(elem_ref.release()));
            }
        }
    }

    /// @brief Destroy the basic_node object and its value storage.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/destructor/
    ~basic_node() noexcept // NOLINT(bugprone-exception-escape)
    {
        if (m_attrs & detail::node_attr_mask::anchoring) {
            if (m_attrs & detail::node_attr_bits::anchor_bit) {
                auto itr = mp_meta->anchor_table.equal_range(m_prop.anchor).first;
                std::advance(itr, detail::node_attr_bits::get_anchor_offset(m_attrs));
                itr->second.m_value.destroy(itr->second.m_attrs & detail::node_attr_mask::value);
                itr->second.m_attrs = detail::node_attr_bits::default_bits;
                itr->second.mp_meta.reset();
            }
        }
        else if ((m_attrs & detail::node_attr_bits::null_bit) == 0) {
            m_value.destroy(m_attrs & detail::node_attr_mask::value);
        }

        m_attrs = detail::node_attr_bits::default_bits;
        mp_meta.reset();
    }

public:
    /// @brief Deserialize the first YAML document in the input into a basic_node object.
    /// @tparam InputType Type of a compatible input.
    /// @param[in] input An input source in the YAML format.
    /// @return The resulting basic_node object deserialized from the input source.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/deserialize/
    template <typename InputType>
    static basic_node deserialize(InputType&& input) {
        return deserializer_type().deserialize(detail::input_adapter(std::forward<InputType>(input)));
    }

    /// @brief Deserialize the first YAML document in the input ranged by the iterators into a basic_node object.
    /// @note
    /// Iterators must satisfy the LegacyInputIterator requirements.
    /// See https://en.cppreference.com/w/cpp/named_req/InputIterator.
    /// @tparam ItrType Type of a compatible iterator
    /// @param[in] begin An iterator to the first element of an input sequence.
    /// @param[in] end An iterator to the past-the-last element of an input sequence.
    /// @return The resulting basic_node object deserialized from the pair of iterators.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/deserialize/
    template <typename ItrType>
    static basic_node deserialize(ItrType begin, ItrType end) {
        return deserializer_type().deserialize(
            detail::input_adapter(std::forward<ItrType>(begin), std::forward<ItrType>(end)));
    }

    /// @brief Deserialize all YAML documents in the input into basic_node objects.
    /// @tparam InputType Type of a compatible input.
    /// @param[in] input An input source in the YAML format.
    /// @return The resulting basic_node objects deserialized from the input.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/deserialize_docs/
    template <typename InputType>
    static std::vector<basic_node> deserialize_docs(InputType&& input) {
        return deserializer_type().deserialize_docs(detail::input_adapter(std::forward<InputType>(input)));
    }

    /// @brief Deserialize all YAML documents in the input ranged by the iterators into basic_node objects.
    /// @tparam ItrType Type of a compatible iterator.
    /// @param[in] begin An iterator to the first element of an input sequence.
    /// @param[in] end An iterator to the past-the-last element of an input sequence.
    /// @return The resulting basic_node objects deserialized from the pair of iterators.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/deserialize_docs/
    template <typename ItrType>
    static std::vector<basic_node> deserialize_docs(ItrType&& begin, ItrType&& end) {
        return deserializer_type().deserialize_docs(
            detail::input_adapter(std::forward<ItrType>(begin), std::forward<ItrType>(end)));
    }

    /// @brief Serialize a basic_node object into a string.
    /// @param[in] node A basic_node object to be serialized.
    /// @return The resulting string object from the serialization of the given node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/serialize/
    static std::string serialize(const basic_node& node) {
        return serializer_type().serialize(node);
    }

    /// @brief Serialize basic_node objects into a string.
    /// @param docs basic_node objects to be serialized.
    /// @return The resulting string object from the serialization of the given nodes.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/serialize_docs/
    static std::string serialize_docs(const std::vector<basic_node>& docs) {
        return serializer_type().serialize_docs(docs);
    }

    /// @brief A factory method for sequence basic_node objects without sequence_type objects.
    /// @return A YAML sequence node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/sequence/
    static basic_node sequence() {
        basic_node node;
        node.m_attrs = detail::node_attr_bits::seq_bit;
        node.m_value.p_seq = detail::create_object<sequence_type>();
        return node;
    } // LCOV_EXCL_LINE

    /// @brief A factory method for sequence basic_node objects with lvalue sequence_type objects.
    /// @param[in] seq A lvalue sequence node value.
    /// @return A YAML sequence node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/sequence/
    static basic_node sequence(const sequence_type& seq) {
        basic_node node;
        node.m_attrs = detail::node_attr_bits::seq_bit;
        node.m_value.p_seq = detail::create_object<sequence_type>(seq);
        return node;
    } // LCOV_EXCL_LINE

    /// @brief A factory method for sequence basic_node objects with rvalue sequence_type objects.
    /// @param[in] seq A rvalue sequence node value.
    /// @return A YAML sequence node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/sequence/
    static basic_node sequence(sequence_type&& seq) {
        basic_node node;
        node.m_attrs = detail::node_attr_bits::seq_bit;
        node.m_value.p_seq = detail::create_object<sequence_type>(std::move(seq));
        return node;
    } // LCOV_EXCL_LINE

    /// @brief A factory method for mapping basic_node objects without mapping_type objects.
    /// @return A YAML mapping node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/mapping/
    static basic_node mapping() {
        basic_node node;
        node.m_attrs = detail::node_attr_bits::map_bit;
        node.m_value.p_map = detail::create_object<mapping_type>();
        return node;
    } // LCOV_EXCL_LINE

    /// @brief A factory method for mapping basic_node objects with lvalue mapping_type objects.
    /// @param[in] map A lvalue mapping node value.
    /// @return A YAML mapping node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/mapping/
    static basic_node mapping(const mapping_type& map) {
        basic_node node;
        node.m_attrs = detail::node_attr_bits::map_bit;
        node.m_value.p_map = detail::create_object<mapping_type>(map);
        return node;
    } // LCOV_EXCL_LINE

    /// @brief A factory method for mapping basic_node objects with rvalue mapping_type objects.
    /// @param[in] map A rvalue mapping node value.
    /// @return A YAML mapping node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/mapping/
    static basic_node mapping(mapping_type&& map) {
        basic_node node;
        node.m_attrs = detail::node_attr_bits::map_bit;
        node.m_value.p_map = detail::create_object<mapping_type>(std::move(map));
        return node;
    } // LCOV_EXCL_LINE

    /// @brief A factory method for alias basic_node objects referencing the given anchor basic_node object.
    /// @note The given anchor basic_node must have a non-empty anchor name.
    /// @param[in] anchor_node A basic_node object with an anchor name.
    /// @return An alias YAML node created from the given anchor node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/alias_of/
    static basic_node alias_of(const basic_node& anchor_node) {
        constexpr detail::node_attr_t anchor_bit = detail::node_attr_bits::anchor_bit;

        if FK_YAML_UNLIKELY (!anchor_node.has_anchor_name() || !(anchor_node.m_attrs & anchor_bit)) {
            throw fkyaml::exception("Cannot create an alias without anchor name.");
        }

        basic_node node = anchor_node;
        node.m_attrs &= ~detail::node_attr_mask::anchoring;
        node.m_attrs |= detail::node_attr_bits::alias_bit;
        return node;
    } // LCOV_EXCL_LINE

public:
    /// @brief A copy assignment operator of the basic_node class.
    /// @param[in] rhs A lvalue basic_node object to be copied with.
    /// @return Reference to this basic_node object.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator=/
    basic_node& operator=(const basic_node& rhs) noexcept {
        basic_node(rhs).swap(*this);
        return *this;
    }

    /// @brief A move assignment operator of the basic_node class.
    /// @param[in] rhs A rvalue basic_node object to be moved from.
    /// @return Reference to this basic_node object.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator=/
    basic_node& operator=(basic_node&& rhs) noexcept {
        basic_node(std::move(rhs)).swap(*this);
        return *this;
    }

    /// @brief A subscript operator of the basic_node class with a key of a compatible type with basic_node.
    /// @tparam KeyType A key type compatible with basic_node
    /// @param key A key to the target value in a sequence/mapping node.
    /// @return The value associated with the given key, or a default basic_node object associated with the given key.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator[]/
    template <
        typename KeyType, detail::enable_if_t<
                              detail::conjunction<
                                  detail::negation<detail::is_basic_node<KeyType>>,
                                  detail::is_node_compatible_type<basic_node, KeyType>>::value,
                              int> = 0>
    basic_node& operator[](KeyType&& key) {
        basic_node& act_node = resolve_reference();

        if FK_YAML_UNLIKELY (act_node.is_scalar_impl()) {
            throw fkyaml::type_error("operator[] is unavailable for a scalar node.", get_type());
        }

        basic_node key_node = std::forward<KeyType>(key);

        if (act_node.is_sequence_impl()) {
            // Do not use is_integer_impl() since n may be an anchor or alias.
            if FK_YAML_UNLIKELY (!key_node.is_integer()) {
                throw fkyaml::type_error(
                    "An argument of operator[] for sequence nodes must be an integer.", get_type());
            }
            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            return act_node.m_value.p_seq->operator[](key_node.get_value<int>());
        }

        FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
        return act_node.m_value.p_map->operator[](std::move(key_node));
    }

    /// @brief A subscript operator of the basic_node class with a key of a compatible type with basic_node.
    /// @tparam KeyType A key type compatible with basic_node
    /// @param key A key to the target value in a sequence/mapping node.
    /// @return The value associated with the given key, or a default basic_node object associated with the given key.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator[]/
    template <
        typename KeyType, detail::enable_if_t<
                              detail::conjunction<
                                  detail::negation<detail::is_basic_node<KeyType>>,
                                  detail::is_node_compatible_type<basic_node, KeyType>>::value,
                              int> = 0>
    const basic_node& operator[](KeyType&& key) const {
        const basic_node& act_node = resolve_reference();

        if FK_YAML_UNLIKELY (act_node.is_scalar_impl()) {
            throw fkyaml::type_error("operator[] is unavailable for a scalar node.", get_type());
        }

        basic_node key_node = std::forward<KeyType>(key);

        if (act_node.is_sequence_impl()) {
            if FK_YAML_UNLIKELY (!key_node.is_integer_impl()) {
                throw fkyaml::type_error(
                    "An argument of operator[] for sequence nodes must be an integer.", get_type());
            }
            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            return act_node.m_value.p_seq->operator[](key_node.get_value<int>());
        }

        FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
        return act_node.m_value.p_map->operator[](std::move(key_node));
    }

    /// @brief A subscript operator of the basic_node class with a basic_node key object.
    /// @tparam KeyType A key type which is a kind of the basic_node template class.
    /// @param key A key to the target value in a sequence/mapping node.
    /// @return The value associated with the given key, or a default basic_node object associated with the given key.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator[]/
    template <typename KeyType, detail::enable_if_t<detail::is_basic_node<KeyType>::value, int> = 0>
    basic_node& operator[](KeyType&& key) {
        if FK_YAML_UNLIKELY (is_scalar()) {
            throw fkyaml::type_error("operator[] is unavailable for a scalar node.", get_type());
        }

        const node_value& node_value = resolve_reference().m_value;

        if (is_sequence()) {
            if FK_YAML_UNLIKELY (!key.is_integer()) {
                throw fkyaml::type_error(
                    "An argument of operator[] for sequence nodes must be an integer.", get_type());
            }
            FK_YAML_ASSERT(node_value.p_seq != nullptr);
            return node_value.p_seq->operator[](std::forward<KeyType>(key).template get_value<int>());
        }

        FK_YAML_ASSERT(node_value.p_map != nullptr);
        return node_value.p_map->operator[](std::forward<KeyType>(key));
    }

    /// @brief A subscript operator of the basic_node class with a basic_node key object.
    /// @tparam KeyType A key type which is a kind of the basic_node template class.
    /// @param key A key to the target value in a sequence/mapping node.
    /// @return The value associated with the given key, or a default basic_node object associated with the given key.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator[]/
    template <typename KeyType, detail::enable_if_t<detail::is_basic_node<KeyType>::value, int> = 0>
    const basic_node& operator[](KeyType&& key) const {
        if FK_YAML_UNLIKELY (is_scalar()) {
            throw fkyaml::type_error("operator[] is unavailable for a scalar node.", get_type());
        }

        const node_value& node_value = resolve_reference().m_value;

        if (is_sequence()) {
            if FK_YAML_UNLIKELY (!key.is_integer()) {
                throw fkyaml::type_error(
                    "An argument of operator[] for sequence nodes must be an integer.", get_type());
            }
            FK_YAML_ASSERT(node_value.p_seq != nullptr);
            return node_value.p_seq->operator[](key.template get_value<int>());
        }

        FK_YAML_ASSERT(node_value.p_map != nullptr);
        return node_value.p_map->operator[](std::forward<KeyType>(key));
    }

    /// @brief An equal-to operator of the basic_node class.
    /// @param rhs A basic_node object to be compared with this basic_node object.
    /// @return true if both types and values are equal, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator_eq/
    bool operator==(const basic_node& rhs) const noexcept {
        const basic_node& lhs = resolve_reference();
        const basic_node& act_rhs = rhs.resolve_reference();

        const detail::node_attr_t lhs_val_bit = lhs.m_attrs & detail::node_attr_mask::value;
        if (lhs_val_bit != (act_rhs.m_attrs & detail::node_attr_mask::value)) {
            return false;
        }

        bool ret = false;
        switch (lhs_val_bit) {
        case detail::node_attr_bits::seq_bit:
            ret = (*(lhs.m_value.p_seq) == *(act_rhs.m_value.p_seq));
            break;
        case detail::node_attr_bits::map_bit:
            ret = (*(lhs.m_value.p_map) == *(act_rhs.m_value.p_map));
            break;
        case detail::node_attr_bits::null_bit:
            // Always true for comparisons between null nodes.
            ret = true;
            break;
        case detail::node_attr_bits::bool_bit:
            ret = (lhs.m_value.boolean == act_rhs.m_value.boolean);
            break;
        case detail::node_attr_bits::int_bit:
            ret = (lhs.m_value.integer == act_rhs.m_value.integer);
            break;
        case detail::node_attr_bits::float_bit:
            ret =
                (std::abs(lhs.m_value.float_val - act_rhs.m_value.float_val) <
                 std::numeric_limits<float_number_type>::epsilon());
            break;
        case detail::node_attr_bits::string_bit:
            ret = (*(lhs.m_value.p_str) == *(act_rhs.m_value.p_str));
            break;
        default:                   // LCOV_EXCL_LINE
            detail::unreachable(); // LCOV_EXCL_LINE
        }

        return ret;
    }

    /// @brief A not-equal-to operator of the basic_node class.
    /// @param rhs A basic_node object to be compared with this basic_node object.
    /// @return true if either types or values are different, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator_ne/
    bool operator!=(const basic_node& rhs) const noexcept {
        return !operator==(rhs);
    }

    /// @brief A less-than operator of the basic_node class.
    /// @param rhs A basic_node object to be compared with this basic_node object.
    /// @return true this basic_node object is less than `rhs`.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator_lt/
    bool operator<(const basic_node& rhs) const noexcept {
        if (operator==(rhs)) {
            return false;
        }

        const basic_node& lhs = resolve_reference();
        const basic_node& act_rhs = rhs.resolve_reference();

        const detail::node_attr_t lhs_val_bit = lhs.m_attrs & detail::node_attr_mask::value;
        const detail::node_attr_t rhs_val_bit = act_rhs.m_attrs & detail::node_attr_mask::value;

        if (lhs_val_bit < rhs_val_bit) {
            return true;
        }

        if (lhs_val_bit != rhs_val_bit) {
            return false;
        }

        bool ret = false;
        switch (lhs_val_bit) {
        case detail::node_attr_bits::seq_bit:
            ret = (*(lhs.m_value.p_seq) < *(act_rhs.m_value.p_seq));
            break;
        case detail::node_attr_bits::map_bit:
            ret = (*(lhs.m_value.p_map) < *(act_rhs.m_value.p_map));
            break;
        case detail::node_attr_bits::null_bit: // LCOV_EXCL_LINE
            // Will not come here since null nodes are always the same.
            detail::unreachable(); // LCOV_EXCL_LINE
        case detail::node_attr_bits::bool_bit:
            // false < true
            ret = (!lhs.m_value.boolean && act_rhs.m_value.boolean);
            break;
        case detail::node_attr_bits::int_bit:
            ret = (lhs.m_value.integer < act_rhs.m_value.integer);
            break;
        case detail::node_attr_bits::float_bit:
            ret = (lhs.m_value.float_val < act_rhs.m_value.float_val);
            break;
        case detail::node_attr_bits::string_bit:
            ret = (*(lhs.m_value.p_str) < *(act_rhs.m_value.p_str));
            break;
        default:                   // LCOV_EXCL_LINE
            detail::unreachable(); // LCOV_EXCL_LINE
        }

        return ret;
    }

    /// @brief A less-than-or-equal-to operator of the basic_node class.
    /// @param rhs A basic_node object to be compared with this basic_node object.
    /// @return true this basic_node object is less than or equal to `rhs`.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator_le/
    bool operator<=(const basic_node& rhs) const noexcept {
        return !rhs.operator<(*this);
    }

    /// @brief A greater-than operator of the basic_node class.
    /// @param rhs A basic_node object to be compared with this basic_node object.
    /// @return true this basic_node object is greater than `rhs`.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator_gt/
    bool operator>(const basic_node& rhs) const noexcept {
        return !operator<=(rhs);
    }

    /// @brief A greater-than-or-equal-to operator of the basic_node class.
    /// @param rhs A basic_node object to be compared with this basic_node object.
    /// @return true this basic_node object is greater than or equal to `rhs`.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/operator_ge/
    bool operator>=(const basic_node& rhs) const noexcept {
        return !operator<(rhs);
    }

public:
    /// @brief Returns the type of the current basic_node value.
    /// @return The type of the YAML node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_type/
    node_type get_type() const noexcept {
        return detail::node_attr_bits::to_node_type(resolve_reference().m_attrs);
    }

    /// @brief Returns the type of the current basic_node value.
    /// @deprecated Use get_type() function. (since 0.3.12)
    /// @return The type of the YAML node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/type/
    FK_YAML_DEPRECATED("Since 0.3.12; Use get_type()")
    node_t type() const noexcept {
        node_type tmp_type = get_type();
        return detail::convert_from_node_type(tmp_type);
    }

    /// @brief Tests whether the current basic_node value is of sequence type.
    /// @return true if the type is sequence, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_sequence/
    bool is_sequence() const noexcept {
        return resolve_reference().is_sequence_impl();
    }

    /// @brief Tests whether the current basic_node value is of mapping type.
    /// @return true if the type is mapping, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_mapping/
    bool is_mapping() const noexcept {
        return resolve_reference().is_mapping_impl();
    }

    /// @brief Tests whether the current basic_node value is of null type.
    /// @return true if the type is null, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_null/
    bool is_null() const noexcept {
        return resolve_reference().is_null_impl();
    }

    /// @brief Tests whether the current basic_node value is of boolean type.
    /// @return true if the type is boolean, false otherwise
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_boolean/
    bool is_boolean() const noexcept {
        return resolve_reference().is_boolean_impl();
    }

    /// @brief Tests whether the current basic_node value is of integer type.
    /// @return true if the type is integer, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_integer/
    bool is_integer() const noexcept {
        return resolve_reference().is_integer_impl();
    }

    /// @brief Tests whether the current basic_node value is of float number type.
    /// @return true if the type is floating point number, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_float_number/
    bool is_float_number() const noexcept {
        return resolve_reference().is_float_number_impl();
    }

    /// @brief Tests whether the current basic_node value is of string type.
    /// @return true if the type is string, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_string/
    bool is_string() const noexcept {
        return resolve_reference().is_string_impl();
    }

    /// @brief Tests whether the current basic_node value is of scalar types.
    /// @return true if the type is scalar, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_scalar/
    bool is_scalar() const noexcept {
        return resolve_reference().is_scalar_impl();
    }

    /// @brief Tests whether the current basic_node is an anchor node.
    /// @return true if the current basic_node is an anchor node, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_anchor/
    bool is_anchor() const noexcept {
        return m_attrs & detail::node_attr_bits::anchor_bit;
    }

    /// @brief Tests whether the current basic_node is an alias node.
    /// @return true if the current basic_node is an alias node, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/is_alias/
    bool is_alias() const noexcept {
        return m_attrs & detail::node_attr_bits::alias_bit;
    }

    /// @brief Tests whether the current basic_node value (sequence, mapping, string) is empty.
    /// @return true if the node value is empty, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/empty/
    bool empty() const {
        const basic_node& act_node = resolve_reference();
        switch (act_node.m_attrs & detail::node_attr_mask::value) {
        case detail::node_attr_bits::seq_bit: {
            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            return act_node.m_value.p_seq->empty();
        }
        case detail::node_attr_bits::map_bit: {
            FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
            return act_node.m_value.p_map->empty();
        }
        case detail::node_attr_bits::string_bit: {
            FK_YAML_ASSERT(act_node.m_value.p_str != nullptr);
            return act_node.m_value.p_str->empty();
        }
        default:
            throw fkyaml::type_error("The target node is not of a container type.", get_type());
        }
    }

    /// @brief Returns the size of the current basic_node value (sequence, mapping, string).
    /// @return The size of a node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/size/
    std::size_t size() const {
        const basic_node& act_node = resolve_reference();
        switch (act_node.m_attrs & detail::node_attr_mask::value) {
        case detail::node_attr_bits::seq_bit:
            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            return act_node.m_value.p_seq->size();
        case detail::node_attr_bits::map_bit:
            FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
            return act_node.m_value.p_map->size();
        case detail::node_attr_bits::string_bit:
            FK_YAML_ASSERT(act_node.m_value.p_str != nullptr);
            return act_node.m_value.p_str->size();
        default:
            throw fkyaml::type_error("The target node is not of a container type.", get_type());
        }
    }

    /// @brief Check whether this basic_node object has a given key in its inner mapping node value.
    /// @tparam KeyType A key type compatible with basic_node.
    /// @param key A key to the target value in the mapping node value.
    /// @return true if the target node is a mapping and has the given key, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/contains/
    template <
        typename KeyType, detail::enable_if_t<
                              detail::disjunction<
                                  detail::is_basic_node<KeyType>,
                                  detail::is_node_compatible_type<basic_node, detail::remove_cvref_t<KeyType>>>::value,
                              int> = 0>
    bool contains(KeyType&& key) const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.m_attrs & detail::node_attr_bits::map_bit) {
            FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
            const auto& map = *act_node.m_value.p_map;
            return map.find(std::forward<KeyType>(key)) != map.end();
        }

        return false;
    }

    /// @brief Get a basic_node object with a key of a compatible type.
    /// @tparam KeyType A key type compatible with basic_node
    /// @param key A key to the target basic_node object in a sequence/mapping node.
    /// @return Reference to the basic_node object associated with the given key.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/at/
    template <
        typename KeyType, detail::enable_if_t<
                              detail::conjunction<
                                  detail::negation<detail::is_basic_node<KeyType>>,
                                  detail::is_node_compatible_type<basic_node, KeyType>>::value,
                              int> = 0>
    basic_node& at(KeyType&& key) {
        basic_node& act_node = resolve_reference();

        if FK_YAML_UNLIKELY (act_node.is_scalar_impl()) {
            throw fkyaml::type_error("at() is unavailable for a scalar node.", get_type());
        }

        basic_node node_key = std::forward<KeyType>(key);

        if (act_node.is_sequence_impl()) {
            if FK_YAML_UNLIKELY (!node_key.is_integer_impl()) {
                throw fkyaml::type_error("An argument of at() for sequence nodes must be an integer.", get_type());
            }

            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            sequence_type& seq = *act_node.m_value.p_seq;
            int index = std::move(node_key).template get_value<int>();
            int size = static_cast<int>(seq.size());
            if FK_YAML_UNLIKELY (index >= size) {
                throw fkyaml::out_of_range(index);
            }
            return seq[index];
        }

        FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
        mapping_type& map = *act_node.m_value.p_map;
        const bool is_found = map.find(node_key) != map.end();
        if FK_YAML_UNLIKELY (!is_found) {
            throw fkyaml::out_of_range(serialize(node_key).c_str());
        }
        return map[std::move(node_key)];
    }

    /// @brief Get a basic_node object with a key of a compatible type.
    /// @tparam KeyType A key type compatible with basic_node
    /// @param key A key to the target basic_node object in a sequence/mapping node.
    /// @return Constant reference to the basic_node object associated with the given key.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/at/
    template <
        typename KeyType, detail::enable_if_t<
                              detail::conjunction<
                                  detail::negation<detail::is_basic_node<KeyType>>,
                                  detail::is_node_compatible_type<basic_node, KeyType>>::value,
                              int> = 0>
    const basic_node& at(KeyType&& key) const {
        const basic_node& act_node = resolve_reference();

        if FK_YAML_UNLIKELY (act_node.is_scalar_impl()) {
            throw fkyaml::type_error("at() is unavailable for a scalar node.", get_type());
        }

        basic_node node_key = std::forward<KeyType>(key);

        if (act_node.is_sequence_impl()) {
            if FK_YAML_UNLIKELY (!node_key.is_integer()) {
                throw fkyaml::type_error("An argument of at() for sequence nodes must be an integer.", get_type());
            }

            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            const sequence_type& seq = *act_node.m_value.p_seq;
            int index = std::move(node_key).template get_value<int>();
            int size = static_cast<int>(seq.size());
            if FK_YAML_UNLIKELY (index >= size) {
                throw fkyaml::out_of_range(index);
            }
            return seq[index];
        }

        FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
        const mapping_type& map = *act_node.m_value.p_map;
        const bool is_found = map.find(node_key) != map.end();
        if FK_YAML_UNLIKELY (!is_found) {
            throw fkyaml::out_of_range(serialize(node_key).c_str());
        }
        return map.at(std::move(node_key));
    }

    /// @brief Get a basic_node object with a basic_node key object.
    /// @tparam KeyType A key type which is a kind of the basic_node template class.
    /// @param key A key to the target basic_node object in a sequence/mapping node.
    /// @return Reference to the basic_node object associated with the given key.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/at/
    template <typename KeyType, detail::enable_if_t<detail::is_basic_node<KeyType>::value, int> = 0>
    basic_node& at(KeyType&& key) {
        basic_node& act_node = resolve_reference();
        if FK_YAML_UNLIKELY (act_node.is_scalar_impl()) {
            throw fkyaml::type_error("at() is unavailable for a scalar node.", get_type());
        }

        if (act_node.is_sequence_impl()) {
            if FK_YAML_UNLIKELY (!key.is_integer()) {
                throw fkyaml::type_error("An argument of at() for sequence nodes must be an integer.", get_type());
            }

            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            sequence_type& seq = *act_node.m_value.p_seq;
            int index = std::forward<KeyType>(key).template get_value<int>();
            int size = static_cast<int>(seq.size());
            if FK_YAML_UNLIKELY (index >= size) {
                throw fkyaml::out_of_range(index);
            }
            return seq[index];
        }

        FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
        mapping_type& map = *act_node.m_value.p_map;
        bool is_found = map.find(key) != map.end();
        if FK_YAML_UNLIKELY (!is_found) {
            throw fkyaml::out_of_range(serialize(key).c_str());
        }
        return map[std::forward<KeyType>(key)];
    }

    /// @brief Get a basic_node object with a basic_node key object.
    /// @tparam KeyType A key type which is a kind of the basic_node template class.
    /// @param key A key to the target basic_node object in a sequence/mapping node.
    /// @return Constant reference to the basic_node object associated with the given key.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/at/
    template <typename KeyType, detail::enable_if_t<detail::is_basic_node<KeyType>::value, int> = 0>
    const basic_node& at(KeyType&& key) const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_UNLIKELY (act_node.is_scalar_impl()) {
            throw fkyaml::type_error("at() is unavailable for a scalar node.", get_type());
        }

        if (act_node.is_sequence_impl()) {
            if FK_YAML_UNLIKELY (!key.is_integer()) {
                throw fkyaml::type_error("An argument of at() for sequence nodes must be an integer.", get_type());
            }

            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            const sequence_type& seq = *act_node.m_value.p_seq;
            int index = std::forward<KeyType>(key).template get_value<int>();
            int size = static_cast<int>(seq.size());
            if FK_YAML_UNLIKELY (index >= size) {
                throw fkyaml::out_of_range(index);
            }
            return seq[index];
        }

        FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
        const mapping_type& map = *act_node.m_value.p_map;
        bool is_found = map.find(key) != map.end();
        if FK_YAML_UNLIKELY (!is_found) {
            throw fkyaml::out_of_range(serialize(key).c_str());
        }
        return map.at(std::forward<KeyType>(key));
    }

    /// @brief Get the YAML version for this basic_node object.
    /// @return The YAML version if already set, `yaml_version_type::VERSION_1_2` otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_yaml_version_type/
    yaml_version_type get_yaml_version_type() const noexcept {
        return mp_meta->is_version_specified ? mp_meta->version : yaml_version_type::VERSION_1_2;
    }

    /// @brief Set the YAML version for this basic_node object.
    /// @param[in] version The target YAML version.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/set_yaml_version_type/
    void set_yaml_version_type(const yaml_version_type version) noexcept {
        mp_meta->version = version;
        mp_meta->is_version_specified = true;
    }

    /// @brief Get the YAML version for this basic_node object.
    /// @deprecated Use get_yaml_version_type() function. (since 0.3.12)
    /// @return The YAML version if already set, `yaml_version_t::VER_1_2` otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_yaml_version/
    FK_YAML_DEPRECATED("Since 0.3.12; Use get_yaml_version_type()")
    yaml_version_t get_yaml_version() const noexcept {
        yaml_version_type tmp_type = get_yaml_version_type();
        return detail::convert_from_yaml_version_type(tmp_type);
    }

    /// @brief Set the YAML version for this basic_node object.
    /// @deprecated Use set_yaml_version_type(yaml_version_type) function. (since 0.3.12)
    /// @param[in] version The target YAML version.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/set_yaml_version/
    FK_YAML_DEPRECATED("Since 0.3.12; Use set_yaml_version_type(const yaml_version_type)")
    void set_yaml_version(const yaml_version_t version) noexcept {
        set_yaml_version_type(detail::convert_to_yaml_version_type(version));
    }

    /// @brief Check whether this basic_node object has already had any anchor name.
    /// @return true if ths basic_node has an anchor name, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/has_anchor_name/
    bool has_anchor_name() const noexcept {
        return (m_attrs & detail::node_attr_mask::anchoring) && !m_prop.anchor.empty();
    }

    /// @brief Get the anchor name associated with this basic_node object.
    /// @note Some anchor name must be set before calling this method. Call has_anchor_name() to see if this basic_node
    /// object has any anchor name.
    /// @return The anchor name associated with the node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_anchor_name/
    const std::string& get_anchor_name() const {
        if FK_YAML_UNLIKELY (!has_anchor_name()) {
            throw fkyaml::exception("No anchor name has been set.");
        }
        return m_prop.anchor;
    }

    /// @brief Add an anchor name to this basic_node object.
    /// @note If this basic_node object has already had any anchor name, the new anchor name will overwrite the old one.
    /// @param[in] anchor_name An anchor name. This should not be empty.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/add_anchor_name/
    void add_anchor_name(const std::string& anchor_name) {
        if (is_anchor()) {
            m_attrs &= ~detail::node_attr_mask::anchoring;
            auto itr = mp_meta->anchor_table.equal_range(m_prop.anchor).first;
            std::advance(itr, detail::node_attr_bits::get_anchor_offset(m_attrs));
            mp_meta.reset();
            itr->second.swap(*this);
            mp_meta->anchor_table.erase(itr);
        }

        auto p_meta = mp_meta;

        basic_node node;
        node.swap(*this);
        p_meta->anchor_table.emplace(anchor_name, std::move(node));

        m_attrs &= ~detail::node_attr_mask::anchoring;
        m_attrs |= detail::node_attr_bits::anchor_bit;
        mp_meta = p_meta;
        const auto offset = static_cast<uint32_t>(mp_meta->anchor_table.count(anchor_name) - 1);
        detail::node_attr_bits::set_anchor_offset(offset, m_attrs);
        m_prop.anchor = anchor_name;
    }

    /// @brief Add an anchor name to this basic_node object.
    /// @note If this basic_node object has already had any anchor name, the new anchor name will overwrite the old one.
    /// @param[in] anchor_name An anchor name. This should not be empty.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/add_anchor_name/
    void add_anchor_name(std::string&& anchor_name) {
        if (is_anchor()) {
            m_attrs &= ~detail::node_attr_mask::anchoring;
            auto itr = mp_meta->anchor_table.equal_range(m_prop.anchor).first;
            std::advance(itr, detail::node_attr_bits::get_anchor_offset(m_attrs));
            mp_meta.reset();
            itr->second.swap(*this);
            mp_meta->anchor_table.erase(itr);
        }

        auto p_meta = mp_meta;

        basic_node node;
        node.swap(*this);
        p_meta->anchor_table.emplace(anchor_name, std::move(node));

        m_attrs &= ~detail::node_attr_mask::anchoring;
        m_attrs |= detail::node_attr_bits::anchor_bit;
        mp_meta = p_meta;
        auto offset = static_cast<uint32_t>(mp_meta->anchor_table.count(anchor_name) - 1);
        detail::node_attr_bits::set_anchor_offset(offset, m_attrs);
        m_prop.anchor = std::move(anchor_name);
    }

    /// @brief Check whether this basic_node object has already had any tag name.
    /// @return true if ths basic_node has a tag name, false otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/has_tag_name/
    bool has_tag_name() const noexcept {
        return !m_prop.tag.empty();
    }

    /// @brief Get the tag name associated with this basic_node object.
    /// @note Some tag name must be set before calling this method. Call has_tag_name() to see if this basic_node
    /// object has any tag name.
    /// @return The tag name associated with the node. It may be empty.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_tag_name/
    const std::string& get_tag_name() const {
        if FK_YAML_UNLIKELY (!has_tag_name()) {
            throw fkyaml::exception("No tag name has been set.");
        }
        return m_prop.tag;
    }

    /// @brief Add a tag name to this basic_node object.
    /// @note If this basic_node object has already had any tag name, the new tag name will overwrite the old one.
    /// @param[in] tag_name A tag name to get associated with this basic_node object.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/add_tag_name/
    void add_tag_name(const std::string& tag_name) {
        m_prop.tag = tag_name;
    }

    /// @brief Add a tag name to this basic_node object.
    /// @note If this basic_node object has already had any tag name, the new tag name will overwrite the old one.
    /// @param[in] tag_name A tag name to get associated with this basic_node object.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/add_tag_name/
    void add_tag_name(std::string&& tag_name) {
        m_prop.tag = std::move(tag_name);
    }

    /// @brief Get the node value object converted into a given type.
    /// @note This function requires T objects to be default constructible. Also, T cannot be either a reference,
    /// pointer or C-style array type.
    /// @tparam T A compatible value type which may be cv-qualified.
    /// @tparam ValueType A compatible value type (T without cv-qualifiers by default).
    /// @return A value converted from this basic_node object.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_value/
    template <
        typename T, typename ValueType = detail::remove_cv_t<T>,
        detail::enable_if_t<
            detail::conjunction<std::is_default_constructible<ValueType>, detail::negation<std::is_pointer<T>>>::value,
            int> = 0>
    T get_value() const noexcept(
        noexcept(std::declval<const basic_node&>().template get_value_impl<ValueType>(std::declval<ValueType&>()))) {
        // emit a compile error if T is either a reference, pointer or C-style array type.
        static_assert(
            !std::is_reference<T>::value,
            "get_value() cannot be called with reference types. "
            "You might want to call one of as_seq(), as_map(), as_bool(), as_int(), as_float() or as_str().");
        static_assert(
            !std::is_array<T>::value,
            "get_value() cannot be called with C-style array types. You might want to call get_value_inplace().");

        auto ret = ValueType();
        resolve_reference().get_value_impl(ret);
        return ret;
    }

    /// @brief Get the node value object converted into a given type. The conversion result is filled into `value_ref`.
    /// @tparam T A compatible value type.
    /// @param value_ref A storage into which the conversion result is filled.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_value_inplace/
    template <typename T>
    void get_value_inplace(T& value_ref) const
        noexcept(noexcept(std::declval<const basic_node&>().template get_value_impl<T>(std::declval<T&>()))) {
        resolve_reference().get_value_impl(value_ref);
    }

    /// @brief Get the node value object converted to a given type. If the conversion fails, this function returns a
    /// given default value instead.
    /// @note This function requires T to be default constructible. Also, T cannot be either a reference, pointer or
    /// C-style array type.
    /// @tparam T A compatible value type which may be cv-qualified.
    /// @tparam U A default value type from which T must be constructible.
    /// @param default_value The default value returned if conversion fails.
    /// @return A value converted from this basic_node object if conversion succeeded, the given default value
    /// otherwise.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_value_or/
    template <
        typename T, typename U,
        detail::enable_if_t<
            detail::conjunction<
                std::is_constructible<T, U>, std::is_default_constructible<T>,
                detail::negation<std::is_pointer<T>>>::value,
            int> = 0>
    T get_value_or(U&& default_value) const noexcept {
        static_assert(
            !std::is_reference<T>::value,
            "get_value_or() cannot be called with reference types. "
            "You might want to call one of as_seq(), as_map(), as_bool(), as_int(), as_float() or as_str().");
        static_assert(
            !std::is_array<T>::value,
            "get_value_or() cannot be called with C-style array types. You might want to call get_value_inplace().");

        // TODO:
        // Ideally, there should be no exception thrown in this kind of function. However, achieving that would require
        // a lot of refactoring and/or some API changes, especially `from_node` interface definition. So, try-catch is
        // used instead for now.
        try {
            return get_value<T>();
        }
        catch (const std::exception& /*unused*/) {
            // Any exception derived from std::exception is interpreted as a conversion failure in some way
            // since user-defined from_node function may throw a different object from a fkyaml::type_error.
            // and std::exception is usually the base class of user-defined exception types.
            return std::forward<U>(default_value);
        }
    }

    /// @brief Explicit reference access to the internally stored YAML node value.
    /// @tparam ReferenceType Reference type to the target YAML node value.
    /// @return Reference to the internally stored YAML node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_value_ref/
    template <typename ReferenceType, detail::enable_if_t<std::is_reference<ReferenceType>::value, int> = 0>
    FK_YAML_DEPRECATED("Since 0.4.3; Use one of as_seq(), as_map(), as_bool(), as_int(), as_float() or as_str()")
    ReferenceType get_value_ref() {
        return get_value_ref_impl(static_cast<detail::add_pointer_t<ReferenceType>>(nullptr));
    }

    /// @brief Explicit reference access to the internally stored YAML node value.
    /// @tparam ReferenceType Constant reference type to the target YAML node value.
    /// @return Constant reference to the internally stored YAML node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/get_value_ref/
    template <
        typename ReferenceType,
        detail::enable_if_t<
            detail::conjunction<
                std::is_reference<ReferenceType>, std::is_const<detail::remove_reference_t<ReferenceType>>>::value,
            int> = 0>
    FK_YAML_DEPRECATED("Since 0.4.3; Use one of as_seq(), as_map(), as_bool(), as_int(), as_float() or as_str()")
    ReferenceType get_value_ref() const {
        return get_value_ref_impl(static_cast<detail::add_pointer_t<ReferenceType>>(nullptr));
    }

    /// @brief Returns reference to the sequence node value.
    /// @throw fkyaml::type_error The node value is not a sequence.
    /// @return Reference to the sequence node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_seq/
    sequence_type& as_seq() {
        basic_node& act_node = resolve_reference(); // NOLINT(misc-const-correctness)
        if FK_YAML_LIKELY (act_node.is_sequence_impl()) {
            return *act_node.m_value.p_seq;
        }
        throw fkyaml::type_error("The node value is not a sequence.", get_type());
    }

    /// @brief Returns constant reference to the sequence node value.
    /// @throw fkyaml::type_error The node value is not a sequence.
    /// @return Constant reference to the sequence node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_seq/
    const sequence_type& as_seq() const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_sequence_impl()) {
            return *act_node.m_value.p_seq;
        }
        throw fkyaml::type_error("The node value is not a sequence.", get_type());
    }

    /// @brief Returns reference to the mapping node value.
    /// @throw fkyaml::type_error The node value is not a mapping.
    /// @return Reference to the mapping node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_map/
    mapping_type& as_map() {
        basic_node& act_node = resolve_reference(); // NOLINT(misc-const-correctness)
        if FK_YAML_LIKELY (act_node.is_mapping_impl()) {
            return *act_node.m_value.p_map;
        }
        throw fkyaml::type_error("The node value is not a mapping.", get_type());
    }

    /// @brief Returns constant reference to the mapping node value.
    /// @throw fkyaml::type_error The node value is not a mapping.
    /// @return Constant reference to the mapping node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_map/
    const mapping_type& as_map() const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_mapping_impl()) {
            return *act_node.m_value.p_map;
        }
        throw fkyaml::type_error("The node value is not a mapping.", get_type());
    }

    /// @brief Returns reference to the boolean node value.
    /// @throw fkyaml::type_error The node value is not a boolean.
    /// @return Reference to the boolean node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_bool/
    boolean_type& as_bool() {
        basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_boolean_impl()) {
            return act_node.m_value.boolean;
        }
        throw fkyaml::type_error("The node value is not a boolean.", get_type());
    }

    /// @brief Returns reference to the boolean node value.
    /// @throw fkyaml::type_error The node value is not a boolean.
    /// @return Constant reference to the boolean node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_bool/
    const boolean_type& as_bool() const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_boolean_impl()) {
            return act_node.m_value.boolean;
        }
        throw fkyaml::type_error("The node value is not a boolean.", get_type());
    }

    /// @brief Checks if the node is an integer that was parsed from a uint64_t value exceeding INT64_MAX.
    /// @return true if the node holds an unsigned integer, false otherwise.
    bool is_uint() const noexcept {
        return resolve_reference().is_uint_impl();
    }

    /// @brief Returns the integer node value as an unsigned 64-bit integer.
    /// This is valid both for nodes where integer_type is unsigned and for nodes where a large
    /// positive decimal scalar (> INT64_MAX) was stored with the uint_bit flag set.
    /// @throw fkyaml::type_error if the node is not a compatible integer.
    /// @return The node value as uint64_t.
    uint64_t as_uint() const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_integer_impl()) {
            // When integer_type is unsigned the stored value IS the uint64_t directly.
            if (std::is_unsigned<integer_type>::value) {
                return static_cast<uint64_t>(act_node.m_value.integer);
            }
            // When integer_type is signed, only uint_bit-marked nodes carry a uint64_t.
            if (act_node.m_attrs & detail::node_attr_bits::uint_bit) {
                return static_cast<uint64_t>(act_node.m_value.integer);
            }
            // Signed values in the non-negative range can be returned safely.
            if (act_node.m_value.integer >= static_cast<integer_type>(0)) {
                return static_cast<uint64_t>(act_node.m_value.integer);
            }
        }
        throw fkyaml::type_error("The node value cannot be represented as an unsigned integer.", get_type());
    }

    /// @brief Returns reference to the integer node value.
    /// @throw fkyaml::type_error The node value is not an integer.
    /// @return Reference to the integer node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_int/
    integer_type& as_int() {
        basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_integer_impl()) {
            if FK_YAML_UNLIKELY (act_node.is_uint_impl()) {
                throw fkyaml::type_error(
                    "The integer value exceeds INT64_MAX and cannot be returned as a signed integer. "
                    "Use as_uint() instead.",
                    get_type());
            }
            return act_node.m_value.integer;
        }
        throw fkyaml::type_error("The node value is not an integer.", get_type());
    }

    /// @brief Returns reference to the integer node value.
    /// @throw fkyaml::type_error The node value is not an integer, or exceeds INT64_MAX.
    /// @return Constant reference to the integer node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_int/
    const integer_type& as_int() const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_integer_impl()) {
            if FK_YAML_UNLIKELY (act_node.is_uint_impl()) {
                throw fkyaml::type_error(
                    "The integer value exceeds INT64_MAX and cannot be returned as a signed integer. "
                    "Use as_uint() instead.",
                    get_type());
            }
            return act_node.m_value.integer;
        }
        throw fkyaml::type_error("The node value is not an integer.", get_type());
    }

    /// @brief Returns reference to the float node value.
    /// @throw fkyaml::type_error The node value is not a float.
    /// @return Reference to the float node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_float/
    float_number_type& as_float() {
        basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_float_number_impl()) {
            return act_node.m_value.float_val;
        }
        throw fkyaml::type_error("The node value is not a float.", get_type());
    }

    /// @brief Returns reference to the float node value.
    /// @throw fkyaml::type_error The node value is not a float.
    /// @return Constant reference to the float node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_float/
    const float_number_type& as_float() const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_float_number_impl()) {
            return act_node.m_value.float_val;
        }
        throw fkyaml::type_error("The node value is not a float.", get_type());
    }

    /// @brief Returns reference to the string node value.
    /// @throw fkyaml::type_error The node value is not a string.
    /// @return Reference to the string node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_str/
    string_type& as_str() {
        basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_string_impl()) {
            return *act_node.m_value.p_str;
        }
        throw fkyaml::type_error("The node value is not a string.", get_type());
    }

    /// @brief Returns reference to the string node value.
    /// @throw fkyaml::type_error The node value is not a string.
    /// @return Constant reference to the string node value.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/as_str/
    const string_type& as_str() const {
        const basic_node& act_node = resolve_reference();
        if FK_YAML_LIKELY (act_node.is_string_impl()) {
            return *act_node.m_value.p_str;
        }
        throw fkyaml::type_error("The node value is not a string.", get_type());
    }

    /// @brief Swaps the internally stored data with the specified basic_node object.
    /// @param[in] rhs A basic_node object to be swapped with.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/swap/
    void swap(basic_node& rhs) noexcept {
        using std::swap;
        swap(m_attrs, rhs.m_attrs);
        swap(mp_meta, rhs.mp_meta);

        node_value tmp {};
        std::memcpy(&tmp, &m_value, sizeof(node_value));
        std::memcpy(&m_value, &rhs.m_value, sizeof(node_value));
        std::memcpy(&rhs.m_value, &tmp, sizeof(node_value));

        swap(m_prop.tag, rhs.m_prop.tag);
        swap(m_prop.anchor, rhs.m_prop.anchor);
    }

    /// @brief Returns an iterator to the first element of a container node (sequence or mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return An iterator to the first element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/begin/
    iterator begin() {
        basic_node& act_node = resolve_reference();
        switch (act_node.m_attrs & detail::node_attr_mask::value) {
        case detail::node_attr_bits::seq_bit:
            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            return {act_node.m_value.p_seq->begin()};
        case detail::node_attr_bits::map_bit:
            FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
            return {act_node.m_value.p_map->begin()};
        default:
            throw fkyaml::type_error("The target node is neither of sequence nor mapping types.", get_type());
        }
    }

    /// @brief Returns a const iterator to the first element of a container node (sequence or mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return A const iterator to the first element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/begin/
    const_iterator begin() const {
        const basic_node& act_node = resolve_reference();
        switch (act_node.m_attrs & detail::node_attr_mask::value) {
        case detail::node_attr_bits::seq_bit:
            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            return {act_node.m_value.p_seq->begin()};
        case detail::node_attr_bits::map_bit:
            FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
            return {act_node.m_value.p_map->begin()};
        default:
            throw fkyaml::type_error("The target node is neither of sequence nor mapping types.", get_type());
        }
    }

    /// @brief Returns a const iterator to the first element of a container node (sequence or mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return A const iterator to the first element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/begin/
    const_iterator cbegin() const {
        return begin();
    }

    /// @brief Returns an iterator to the past-the-last element of a container node (sequence or mapping).
    /// @throw `type_error` if the basic_node value is not of container types.
    /// @return An iterator to the past-the-last element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/end/
    iterator end() {
        basic_node& act_node = resolve_reference();
        switch (act_node.m_attrs & detail::node_attr_mask::value) {
        case detail::node_attr_bits::seq_bit:
            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            return {act_node.m_value.p_seq->end()};
        case detail::node_attr_bits::map_bit:
            FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
            return {act_node.m_value.p_map->end()};
        default:
            throw fkyaml::type_error("The target node is neither of sequence nor mapping types.", get_type());
        }
    }

    /// @brief Returns a const iterator to the past-the-last element of a container node (sequence or mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return A const iterator to the past-the-last element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/end/
    const_iterator end() const {
        const basic_node& act_node = resolve_reference();
        switch (act_node.m_attrs & detail::node_attr_mask::value) {
        case detail::node_attr_bits::seq_bit:
            FK_YAML_ASSERT(act_node.m_value.p_seq != nullptr);
            return {act_node.m_value.p_seq->end()};
        case detail::node_attr_bits::map_bit:
            FK_YAML_ASSERT(act_node.m_value.p_map != nullptr);
            return {act_node.m_value.p_map->end()};
        default:
            throw fkyaml::type_error("The target node is neither of sequence nor mapping types.", get_type());
        }
    }

    /// @brief Returns a const iterator to the past-the-last element of a container node (sequence or mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return A const iterator to the past-the-last element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/end/
    const_iterator cend() const {
        return end();
    }

    /// @brief Returns an iterator to the reverse-beginning (i.e., last) element of a container node (sequence or
    /// mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return An iterator to the reverse-beginning element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/rbegin/
    reverse_iterator rbegin() {
        return {end()};
    }

    /// @brief Returns a const iterator to the reverse-beginning (i.e., last) element of a container node (sequence or
    /// mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return A const iterator to the reverse-beginning element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/rbegin/
    const_reverse_iterator rbegin() const {
        return {end()};
    }

    /// @brief Returns a const iterator to the reverse-beginning (i.e., last) element of a container node (sequence or
    /// mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return A const iterator to the reverse-beginning element of a container node.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/rbegin/
    const_reverse_iterator crbegin() const {
        return rbegin();
    }

    /// @brief Returns an iterator to the reverse-end (i.e., one before the first) element of a container node (sequence
    /// or mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return An iterator to the reverse-end element.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/rend/
    reverse_iterator rend() {
        return {begin()};
    }

    /// @brief Returns a const iterator to the reverse-end (i.e., one before the first) element of a container node
    /// (sequence or mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return A const iterator to the reverse-end element.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/rend/
    const_reverse_iterator rend() const {
        return {begin()};
    }

    /// @brief Returns a const iterator to the reverse-end (i.e., one before the first) element of a container node
    /// (sequence or mapping).
    /// @throw `type_error` if this basic_node is neither a sequence nor mapping node.
    /// @return A const iterator to the reverse-end element.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/rend/
    const_reverse_iterator crend() const {
        return rend();
    }

    /// @brief Returns a range of mapping entries.
    /// @throw `type_error` if this basic_node is not a mapping.
    /// @return A range of mapping entries.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/map_items/
    map_range map_items() {
        if FK_YAML_UNLIKELY (!is_mapping()) {
            throw type_error("map_items() cannot be called on a non-mapping node.", get_type());
        }
        return {*this};
    }

    /// @brief Returns a const range of mapping entries.
    /// @throw `type_error` if this basic_node is not a mapping.
    /// @return A const range of mapping entries.
    /// @sa https://fktn-k.github.io/fkYAML/api/basic_node/map_items/
    const_map_range map_items() const {
        if FK_YAML_UNLIKELY (!is_mapping()) {
            throw type_error("map_items() cannot be called on a non-mapping node.", get_type());
        }
        return {*this};
    }

private:
    /// @brief Resolves anchor/alias reference and returns reference to an actual value node.
    /// @return Reference to an actual value node.
    basic_node& resolve_reference() {
        if FK_YAML_UNLIKELY (has_anchor_name()) {
            auto itr = mp_meta->anchor_table.equal_range(m_prop.anchor).first;
            std::advance(itr, detail::node_attr_bits::get_anchor_offset(m_attrs));
            return itr->second;
        }
        return *this;
    }

    /// @brief Resolves anchor/alias reference and returns const reference to an actual value node.
    /// @return Const reference to an actual value node.
    const basic_node& resolve_reference() const {
        if FK_YAML_UNLIKELY (has_anchor_name()) {
            auto itr = mp_meta->anchor_table.equal_range(m_prop.anchor).first;
            std::advance(itr, detail::node_attr_bits::get_anchor_offset(m_attrs));
            return itr->second;
        }
        return *this;
    }

    bool is_sequence_impl() const noexcept {
        return m_attrs & detail::node_attr_bits::seq_bit;
    }

    bool is_mapping_impl() const noexcept {
        return m_attrs & detail::node_attr_bits::map_bit;
    }

    bool is_null_impl() const noexcept {
        return m_attrs & detail::node_attr_bits::null_bit;
    }

    bool is_boolean_impl() const noexcept {
        return m_attrs & detail::node_attr_bits::bool_bit;
    }

    bool is_integer_impl() const noexcept {
        return m_attrs & detail::node_attr_bits::int_bit;
    }

    bool is_uint_impl() const noexcept {
        // Both int_bit and uint_bit must be set: this node stores a uint64_t value
        // whose bit pattern was placed into the signed integer_type field.
        return (m_attrs & detail::node_attr_bits::int_bit) && (m_attrs & detail::node_attr_bits::uint_bit);
    }

    bool is_float_number_impl() const noexcept {
        return m_attrs & detail::node_attr_bits::float_bit;
    }

    bool is_string_impl() const noexcept {
        return m_attrs & detail::node_attr_bits::string_bit;
    }

    bool is_scalar_impl() const noexcept {
        return m_attrs & detail::node_attr_bits::scalar_bits;
    }

    template <
        typename ValueType, detail::enable_if_t<detail::negation<detail::is_basic_node<ValueType>>::value, int> = 0>
    void get_value_impl(ValueType& v) const
        noexcept(noexcept(ConverterType<ValueType, void>::from_node(std::declval<const basic_node&>(), v))) {
        ConverterType<ValueType, void>::from_node(*this, v);
    }

    template <typename ValueType, detail::enable_if_t<detail::is_basic_node<ValueType>::value, int> = 0>
    void get_value_impl(ValueType& v) const {
        v = *this;
    }

    /// @brief Returns reference to the sequence node value.
    /// @throw fkyaml::exception The node value is not a sequence.
    /// @return Reference to the sequence node value.
    sequence_type& get_value_ref_impl(sequence_type* /*unused*/) {
        return as_seq();
    }

    /// @brief Returns constant reference to the sequence node value.
    /// @throw fkyaml::exception The node value is not a sequence.
    /// @return Constant reference to the sequence node value.
    const sequence_type& get_value_ref_impl(const sequence_type* /*unused*/) const {
        return as_seq();
    }

    /// @brief Returns reference to the mapping node value.
    /// @throw fkyaml::exception The node value is not a mapping.
    /// @return Reference to the mapping node value.
    mapping_type& get_value_ref_impl(mapping_type* /*unused*/) {
        return as_map();
    }

    /// @brief Returns constant reference to the mapping node value.
    /// @throw fkyaml::exception The node value is not a mapping.
    /// @return Constant reference to the mapping node value.
    const mapping_type& get_value_ref_impl(const mapping_type* /*unused*/) const {
        return as_map();
    }

    /// @brief Returns reference to the boolean node value.
    /// @throw fkyaml::exception The node value is not a boolean.
    /// @return Reference to the boolean node value.
    boolean_type& get_value_ref_impl(boolean_type* /*unused*/) {
        return as_bool();
    }

    /// @brief Returns reference to the boolean node value.
    /// @throw fkyaml::exception The node value is not a boolean.
    /// @return Constant reference to the boolean node value.
    const boolean_type& get_value_ref_impl(const boolean_type* /*unused*/) const {
        return as_bool();
    }

    /// @brief Returns reference to the integer node value.
    /// @throw fkyaml::exception The node value is not an integer.
    /// @return Reference to the integer node value.
    integer_type& get_value_ref_impl(integer_type* /*unused*/) {
        return as_int();
    }

    /// @brief Returns reference to the integer node value.
    /// @throw fkyaml::exception The node value is not an integer.
    /// @return Constant reference to the integer node value.
    const integer_type& get_value_ref_impl(const integer_type* /*unused*/) const {
        return as_int();
    }

    /// @brief Returns reference to the floating point number node value.
    /// @throw fkyaml::exception The node value is not a floating point number.
    /// @return Reference to the floating point number node value.
    float_number_type& get_value_ref_impl(float_number_type* /*unused*/) {
        return as_float();
    }

    /// @brief Returns reference to the floating point number node value.
    /// @throw fkyaml::exception The node value is not a floating point number.
    /// @return Constant reference to the floating point number node value.
    const float_number_type& get_value_ref_impl(const float_number_type* /*unused*/) const {
        return as_float();
    }

    /// @brief Returns reference to the string node value.
    /// @throw fkyaml::exception The node value is not a string.
    /// @return Reference to the string node value.
    string_type& get_value_ref_impl(string_type* /*unused*/) {
        return as_str();
    }

    /// @brief Returns reference to the string node value.
    /// @throw fkyaml::exception The node value is not a string.
    /// @return Constant reference to the string node value.
    const string_type& get_value_ref_impl(const string_type* /*unused*/) const {
        return as_str();
    }

    /// The current node attributes.
    detail::node_attr_t m_attrs {detail::node_attr_bits::default_bits};
    /// The shared set of YAML directives applied to this node.
    mutable std::shared_ptr<detail::document_metainfo<basic_node>> mp_meta {
        // NOLINTNEXTLINE(bugprone-unhandled-exception-at-new)
        std::shared_ptr<detail::document_metainfo<basic_node>>(new detail::document_metainfo<basic_node>())};
    /// The current node value.
    node_value m_value {};
    /// The property set of this node.
    detail::node_property m_prop {};
};

/// @brief Swap function for basic_node objects.
/// @param[in] lhs A left-side-hand basic_node object to be swapped with.
/// @param[in] rhs A right-side-hand basic_node object to be swapped with.
/// @sa https://fktn-k.github.io/fkYAML/api/swap/
template <
    template <typename, typename...> class SequenceType, template <typename, typename, typename...> class MappingType,
    typename BooleanType, typename IntegerType, typename FloatNumberType, typename StringType,
    template <typename, typename = void> class ConverterType>
inline void swap(
    basic_node<SequenceType, MappingType, BooleanType, IntegerType, FloatNumberType, StringType, ConverterType>& lhs,
    basic_node<SequenceType, MappingType, BooleanType, IntegerType, FloatNumberType, StringType, ConverterType>&
        rhs) noexcept(noexcept(lhs.swap(rhs))) {
    lhs.swap(rhs);
}

/// @brief Insertion operator for basic_node template class. A wrapper for the serialization feature.
/// @param[in] os An output stream object.
/// @param[in] n A basic_node object.
/// @return Reference to the output stream object `os`.
/// @sa https://fktn-k.github.io/fkYAML/api/basic_node/insertion_operator/
template <
    template <typename, typename...> class SequenceType, template <typename, typename, typename...> class MappingType,
    typename BooleanType, typename IntegerType, typename FloatNumberType, typename StringType,
    template <typename, typename = void> class ConverterType>
inline std::ostream& operator<<(
    std::ostream& os,
    const basic_node<SequenceType, MappingType, BooleanType, IntegerType, FloatNumberType, StringType, ConverterType>&
        n) {
    os << basic_node<SequenceType, MappingType, BooleanType, IntegerType, FloatNumberType, StringType, ConverterType>::
            serialize(n);
    return os;
}

/// @brief Extraction operator for basic_node template class. A wrapper for the deserialization feature with input
/// streams.
/// @param[in] is An input stream object.
/// @param[in] n A basic_node object.
/// @return Reference to the input stream object `is`.
/// @sa https://fktn-k.github.io/fkYAML/api/basic_node/extraction_operator/
template <
    template <typename, typename...> class SequenceType, template <typename, typename, typename...> class MappingType,
    typename BooleanType, typename IntegerType, typename FloatNumberType, typename StringType,
    template <typename, typename = void> class ConverterType>
inline std::istream& operator>>(
    std::istream& is,
    basic_node<SequenceType, MappingType, BooleanType, IntegerType, FloatNumberType, StringType, ConverterType>& n) {
    n = basic_node<SequenceType, MappingType, BooleanType, IntegerType, FloatNumberType, StringType, ConverterType>::
        deserialize(is);
    return is;
}

/// @brief namespace for user-defined literals for the fkYAML library.
inline namespace literals {
/// @brief namespace for user-defined literals for YAML node objects.
inline namespace yaml_literals {

// Whitespace before the literal operator identifier is deprecated in C++23 or better but required in C++11.
// Ignore the warning as a workaround. https://github.com/fktn-k/fkYAML/pull/417
#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated"
#endif

#if defined(__GNUC__) && (__GNUC__ > 6)
#define FK_YAML_QUOTE_OPERATOR operator""_yaml
#else
#define FK_YAML_QUOTE_OPERATOR operator"" _yaml
#endif

/// @brief The user-defined string literal which deserializes a `char` array into a `node` object.
/// @param s An input `char` array.
/// @param n The size of `s`.
/// @return The resulting `node` object deserialized from `s`.
/// @sa https://fktn-k.github.io/fkYAML/api/operator_literal_yaml/
inline fkyaml::node FK_YAML_QUOTE_OPERATOR(const char* s, std::size_t n) {
    return fkyaml::node::deserialize(s, s + n);
}

/// @brief The user-defined string literal which deserializes a `char16_t` array into a `node` object.
/// @param s An input `char16_t` array.
/// @param n The size of `s`.
/// @return The resulting `node` object deserialized from `s`.
/// @sa https://fktn-k.github.io/fkYAML/api/operator_literal_yaml/
inline fkyaml::node FK_YAML_QUOTE_OPERATOR(const char16_t* s, std::size_t n) {
    return fkyaml::node::deserialize(s, s + n);
}

/// @brief The user-defined string literal which deserializes a `char32_t` array into a `node` object.
/// @param s An input `char32_t` array.
/// @param n The size of `s`.
/// @return The resulting `node` object deserialized from `s`.
/// @sa https://fktn-k.github.io/fkYAML/api/operator_literal_yaml/
inline fkyaml::node FK_YAML_QUOTE_OPERATOR(const char32_t* s, std::size_t n) {
    return fkyaml::node::deserialize(s, s + n);
}

#if FK_YAML_HAS_CHAR8_T
/// @brief The user-defined string literal which deserializes a `char8_t` array into a `node` object.
/// @param s An input `char8_t` array.
/// @param n The size of `s`.
/// @return The resulting `node` object deserialized from `s`.
inline fkyaml::node FK_YAML_QUOTE_OPERATOR(const char8_t* s, std::size_t n) {
    return fkyaml::node::deserialize(s, s + n);
}

#if defined(__clang__)
#pragma clang diagnostic pop
#endif

#endif

} // namespace yaml_literals
} // namespace literals

FK_YAML_NAMESPACE_END

namespace std {

template <
    template <typename, typename...> class SequenceType, template <typename, typename, typename...> class MappingType,
    typename BooleanType, typename IntegerType, typename FloatNumberType, typename StringType,
    template <typename, typename = void> class ConverterType>
// NOLINTNEXTLINE(cert-dcl58-cpp)
struct hash<fkyaml::basic_node<
    SequenceType, MappingType, BooleanType, IntegerType, FloatNumberType, StringType, ConverterType>> {
    using node_t = fkyaml::basic_node<
        SequenceType, MappingType, BooleanType, IntegerType, FloatNumberType, StringType, ConverterType>;

    std::size_t operator()(const node_t& n) const {
        using boolean_type = typename node_t::boolean_type;
        using integer_type = typename node_t::integer_type;
        using float_number_type = typename node_t::float_number_type;
        using string_type = typename node_t::string_type;

        const auto type = n.get_type();

        std::size_t seed = 0;
        hash_combine(seed, std::hash<uint8_t>()(static_cast<uint8_t>(type)));

        switch (type) {
        case fkyaml::node_type::SEQUENCE:
            hash_combine(seed, n.size());
            for (const auto& elem : n) {
                hash_combine(seed, operator()(elem));
            }
            return seed;

        case fkyaml::node_type::MAPPING:
            hash_combine(seed, n.size());
            for (auto itr = n.begin(), end_itr = n.end(); itr != end_itr; ++itr) {
                hash_combine(seed, operator()(itr.key()));
                hash_combine(seed, operator()(itr.value()));
            }
            return seed;

        case fkyaml::node_type::NULL_OBJECT:
            hash_combine(seed, 0);
            return seed;
        case fkyaml::node_type::BOOLEAN:
            hash_combine(seed, std::hash<boolean_type>()(n.template get_value<boolean_type>()));
            return seed;
        case fkyaml::node_type::INTEGER:
            hash_combine(seed, std::hash<integer_type>()(n.template get_value<integer_type>()));
            return seed;
        case fkyaml::node_type::FLOAT:
            hash_combine(seed, std::hash<float_number_type>()(n.template get_value<float_number_type>()));
            return seed;
        case fkyaml::node_type::STRING:
            hash_combine(seed, std::hash<string_type>()(n.template get_value<string_type>()));
            return seed;
        default:                           // LCOV_EXCL_LINE
            fkyaml::detail::unreachable(); // LCOV_EXCL_LINE
        }
    }

private:
    // taken from boost::hash_combine
    FK_YAML_NO_SANITIZE("unsigned-shift-base", "unsigned-integer-overflow")
    static void hash_combine(std::size_t& seed, std::size_t v) {
        seed ^= v + 0x9e3779b9 + (seed << 6u) + (seed >> 2u);
    }
};

} // namespace std

#endif /* FK_YAML_NODE_HPP */

fktn-k / fkYAML / 28925996281

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