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4303ba674d
Add json_document and json_view, a read-only, zero-copy index of a JSON text, as the first public slice of the zero-copy view (#5295). A parse produces a flat array of 16-byte nodes in document order, one per value and one per object key. Strings stay in the source text; escaped strings are decoded into an arena. Integers are converted while their digits are in the cache; floats keep only their digit layout and are converted on read. Containers store the size of their subtree, so a reader can step over one in constant time. A document makes a handful of allocations, however many values it has. The parser accepts exactly what json::parse accepts, with every combination of ignore_comments and ignore_trailing_commas, with and without a trailing NUL, and under JSON_STRICT_NUL_HANDLING. It is portable C++11 and does not depend on byte order. basic_json_document adds parse, parse_copy, accept, read (reuses a document's memory), root, is_discarded, source, owns_source, node_count, memory_usage, and shrink_to_fit. basic_json_view adds type, the is_* queries, operator bool, size, empty, materialize, and source_offset. A parse error throws the same exception basic_json::parse would throw for the same input, message and position included. detail::abi_config keeps JSON_STRICT_NUL_HANDLING and JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON readable after json.hpp undefines them, in the ABI namespace so they always match the basic_json in use. A NUL byte that ends a // comment is the end of the input, as in parse() since #5696. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
89 lines
3.0 KiB
C++
89 lines
3.0 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 <string> // basic_string, char_traits, string
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#include <type_traits> // decay, integral_constant, is_array, is_lvalue_reference, is_pointer, is_same, remove_reference
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#include <utility> // forward
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#include <nlohmann/json.hpp>
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#include <nlohmann/detail/view/macro_scope.hpp>
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#if NLOHMANN_VIEW_HAS_CPP_17
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#include <string_view> // string_view
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#endif
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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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/// how a document takes its input
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enum class input_kind
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{
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move_string, ///< rvalue std::string: owned without a copy
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c_string, ///< const char* (NUL-terminated): borrowed
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char_array, ///< char array (e.g. a string literal): borrowed
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borrow_range, ///< lvalue contiguous byte container, or std::string_view: borrowed
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copy_range, ///< rvalue contiguous byte container: copied
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adapter, ///< anything else parse() accepts (streams, wide strings, ...): read into a buffer
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};
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template<typename InputType>
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struct classify_input
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{
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using R = typename std::remove_reference<InputType>::type;
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using D = typename std::decay<InputType>::type;
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static constexpr bool is_rvalue = !std::is_lvalue_reference<InputType>::value;
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static constexpr bool is_bytes = is_contiguous_byte_container<D>::value;
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#if NLOHMANN_VIEW_HAS_CPP_17
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static constexpr bool is_string_view = std::is_same<D, std::string_view>::value;
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#else
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static constexpr bool is_string_view = false;
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#endif
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// NOLINTBEGIN(readability-avoid-nested-conditional-operator): a constant expression of C++11
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static constexpr input_kind value =
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std::is_array<R>::value ? input_kind::char_array
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: std::is_pointer<D>::value ? input_kind::c_string
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: (is_rvalue && std::is_same<D, std::string>::value) ? input_kind::move_string
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: (is_bytes && (!is_rvalue || is_string_view)) ? input_kind::borrow_range
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: is_bytes ? input_kind::copy_range
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: input_kind::adapter;
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// NOLINTEND(readability-avoid-nested-conditional-operator)
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};
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/// std::basic_string guarantees a NUL at data()[size()] (the parser's sentinel)
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template<typename T>
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struct is_std_string : std::false_type {};
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template<typename Traits, typename Alloc>
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struct is_std_string<std::basic_string<char, Traits, Alloc>> : std::true_type {};
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/// drain a json input adapter (UTF-16/32 inputs arrive as UTF-8)
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template<typename Adapter>
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std::string collect_adapter(Adapter ia)
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{
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std::string buf;
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for (;;)
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{
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const auto ch = ia.get_character();
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if (ch == std::char_traits<char>::eof())
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{
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break;
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}
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buf.push_back(static_cast<char>(ch));
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}
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return buf;
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}
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} // namespace view
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} // namespace detail
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NLOHMANN_JSON_NAMESPACE_END
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