mirror of
https://github.com/nlohmann/json.git
synced 2026-10-06 22:47:13 +00:00
Niels Lohmann
0adb7783a4
Give basic_json_view the read-only access functions of basic_json: operator[] and at() with keys and indices, front()/back(), find(), contains(), count(), begin()/end() and cbegin()/cend(), items() with structured bindings from C++17 on, and type_name(). Exceptions have the ids and messages of the const functions of basic_json. Where basic_json has undefined behavior the view answers safely: operator[] with a missing key or an out-of-range index returns a discarded view, and front()/back() of an empty container throw invalid_iterator.214. Objects are iterated in document order, and all members are visited; duplicate-key lookups find the first member (as yyjson and simdjson do), while parse(), materialize(), and the map conversions keep the last value, as parse() does. Keys of up to 16 bytes are compared with two overlapping loads. Add value conversions: get<T>()/get_to() for arithmetic types, bool, nullptr_t, strings (std::basic_string copied, string_view_t without a copy), BasicJsonType, views, std::vector, and maps with string keys; get_string() for the string without a copy; number_token() for the number exactly as written in the source; value() with keys and JSON pointers; and operator[]/at()/ contains() with JSON pointers. Everything else, including types with from_json(), goes through materialize() of that subtree. get<T>() of arithmetic types is inlined down to the conversion, so reading an integer needs no call. detail::json_pointer_access exposes a pointer's reference tokens to code outside basic_json. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
109 lines
3.5 KiB
C++
109 lines
3.5 KiB
C++
// __ _____ _____ _____
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// __| | __| | | | JSON for Modern C++
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// | | |__ | | | | | | version 3.12.0
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// |_____|_____|_____|_|___| https://github.com/nlohmann/json
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//
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// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
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// SPDX-License-Identifier: MIT
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#pragma once
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#include <cstdint> // int64_t
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#include <map> // map
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#include <string> // basic_string
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#include <type_traits> // enable_if, is_constructible
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#include <unordered_map> // unordered_map
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#include <vector> // vector
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#include <nlohmann/json.hpp>
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#include <nlohmann/detail/view/document_data.hpp>
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#include <nlohmann/detail/view/errors.hpp>
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#include <nlohmann/detail/view/macro_scope.hpp>
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#include <nlohmann/detail/view/node.hpp>
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#include <nlohmann/detail/view/number.hpp>
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NLOHMANN_JSON_NAMESPACE_BEGIN
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namespace detail
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{
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namespace view
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{
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/// selects a conversion by its target type
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template<typename T>
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struct value_tag {};
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/*!
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@brief the number or boolean of a node converted to an arithmetic type
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As basic_json's get<T>() for arithmetic types: integers and floats are
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converted with static_cast, booleans give 0 or 1, and other types throw
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type_error.302.
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*/
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template<typename T, typename BasicJsonType>
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NLOHMANN_VIEW_ALWAYS_INLINE T arithmetic_value(const document_data& d, const node& n)
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{
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switch (static_cast<value_t>(n.kind))
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{
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case value_t::number_unsigned:
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return static_cast<T>(static_cast<typename BasicJsonType::number_unsigned_t>(integer_bits(n)));
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case value_t::number_integer:
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return static_cast<T>(static_cast<typename BasicJsonType::number_integer_t>(static_cast<std::int64_t>(integer_bits(n))));
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case value_t::number_float:
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return static_cast<T>(float_value<typename BasicJsonType::number_float_t>(d.str(n), n));
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case value_t::boolean:
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return static_cast<T>((n.flags & node_flags::is_true) != 0);
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case value_t::null:
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case value_t::object:
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case value_t::array:
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case value_t::string:
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case value_t::binary:
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case value_t::discarded:
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default:
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throw_type_error(302, "type must be number, but is ", value_type_name(static_cast<value_t>(n.kind)));
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}
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}
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/// std::vector from an array, element by element (type_error.302 otherwise)
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template<typename View, typename U, typename A>
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std::vector<U, A> vector_value(const View& v)
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{
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if (NLOHMANN_VIEW_UNLIKELY(!v.is_array()))
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{
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throw_type_error(302, "type must be array, but is ", v.type_name());
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}
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std::vector<U, A> r;
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r.reserve(v.size());
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for (const View e : v)
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{
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r.push_back(e.template get<U>());
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}
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return r;
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}
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/// a map with string keys from an object; with duplicate keys, the last
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/// value is kept, as parse() does (type_error.302 for other types)
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template<typename Map, typename View>
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Map map_value(const View& v)
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{
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if (NLOHMANN_VIEW_UNLIKELY(!v.is_object()))
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{
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throw_type_error(302, "type must be object, but is ", v.type_name());
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}
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Map r;
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for (auto it = v.begin(); it != v.end(); ++it)
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{
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const auto key = it.key();
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r[typename Map::key_type(key.data(), key.size())] = it.value().template get<typename Map::mapped_type>();
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}
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return r;
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}
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/// whether a map type is read member by member (its keys are made from
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/// characters and a length); other maps go through basic_json
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template<typename Key>
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struct is_string_key : std::is_constructible<Key, const char*, std::size_t> {};
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} // namespace view
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} // namespace detail
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NLOHMANN_JSON_NAMESPACE_END
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