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8b58c8cd7c
basic_json_view gains get<T>(), get_to(), value() with keys and JSON pointers, and operator[], at(), and contains() with JSON pointers, plus two functions basic_json has no counterpart for: - get_string(): the string without a copy (a string_view into the source, or into the decoded strings for strings with escapes) - number_token(): the text of a number as it appears in the source get<T>() converts arithmetic types, strings (also string_view_t), std::nullptr_t, std::vector, maps with string keys, and views directly; floats are converted from the digit layout recorded by the parser with the library's conversion chain, so the values are bit-identical to parse(). Other types, including user types with from_json(), go through materialize(). The exceptions are those of basic_json, message included. Where const basic_json has undefined behavior (a missing key or an index out of range with operator[] and a JSON pointer), the result is a discarded view; value() returns the default wherever basic_json catches out_of_range, and contains() never throws. Array indices of JSON pointers follow json_pointer's rules (parse_error.106/109, out_of_range.404/410). Tests compare the conversions of 2,000 generated documents, 20,000 float tokens (double and float, bit for bit), and every JSON pointer of 1,000 documents with basic_json, and the exceptions for malformed pointers. 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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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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