Add json_document and json_view: parse, accept, types, materialize

The public classes of the zero-copy view (#5295), in the new header <nlohmann/json_view.hpp>: - basic_json_document<BasicJsonType>: parse (borrowing contiguous byte inputs, owning rvalue strings, streams, and other inputs), parse_copy, accept, read, root, is_discarded, source, owns_source, node_count, memory_usage, shrink_to_fit - basic_json_view<BasicJsonType>: type and the is_* queries, size, empty, materialize (the value parse() would produce, built by the same SAX handler), source_offset - the aliases json_document, json_view, ordered_json_document, and ordered_json_view A parse error throws the exception basic_json::parse would throw for the same input: the library parser is run on the failing input, so messages, positions, and exception ids are the same. Inputs of 4 GiB or more are rejected with out_of_range.416. The single header single_include/nlohmann/json_view.hpp keeps including json.hpp; make amalgamate, check-amalgamation, include.zip, and release handle it. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-04 05:30:31 +00:00 · 2026-09-30 20:57:43 +02:00
parent e96e2982a5
commit cf352d4ef5
10 changed files with 3623 additions and 6 deletions
@@ -0,0 +1,86 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <string> // basic_string, char_traits, string
+#include <type_traits> // decay, integral_constant, is_array, is_lvalue_reference, is_pointer, is_same, remove_reference
+#include <utility> // forward
+
+#include <nlohmann/json.hpp>
+#include <nlohmann/detail/view/macro_scope.hpp>
+
+#if NLOHMANN_VIEW_HAS_CPP_17
+    #include <string_view> // string_view
+#endif
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+namespace view
+{
+
+/// how a document takes its input
+enum class input_kind
+{
+    move_string,  ///< rvalue std::string: owned without a copy
+    c_string,     ///< const char* (NUL-terminated): borrowed
+    char_array,   ///< char array (e.g. a string literal): borrowed
+    borrow_range, ///< lvalue contiguous byte container, or std::string_view: borrowed
+    copy_range,   ///< rvalue contiguous byte container: copied
+    adapter,      ///< anything else parse() accepts (streams, wide strings, ...): read into a buffer
+};
+
+template<typename InputType>
+struct classify_input
+{
+    using R = typename std::remove_reference<InputType>::type;
+    using D = typename std::decay<InputType>::type;
+    static constexpr bool is_rvalue = !std::is_lvalue_reference<InputType>::value;
+    static constexpr bool is_bytes = is_contiguous_byte_container<D>::value;
+#if NLOHMANN_VIEW_HAS_CPP_17
+    static constexpr bool is_string_view = std::is_same<D, std::string_view>::value;
+#else
+    static constexpr bool is_string_view = false;
+#endif
+    static constexpr input_kind value =
+        std::is_array<R>::value ? input_kind::char_array
+        : std::is_pointer<D>::value ? input_kind::c_string
+        : (is_rvalue && std::is_same<D, std::string>::value) ? input_kind::move_string
+        : (is_bytes && (!is_rvalue || is_string_view)) ? input_kind::borrow_range
+        : is_bytes ? input_kind::copy_range
+        : input_kind::adapter;
+};
+
+/// std::basic_string guarantees a NUL at data()[size()] (the parser's sentinel)
+template<typename T>
+struct is_std_string : std::false_type {};
+
+template<typename Traits, typename Alloc>
+struct is_std_string<std::basic_string<char, Traits, Alloc>> : std::true_type {};
+
+/// drain a json input adapter (UTF-16/32 inputs arrive as UTF-8)
+template<typename Adapter>
+std::string collect_adapter(Adapter&& ia)
+{
+    std::string buf;
+    for (;;)
+    {
+        const auto ch = ia.get_character();
+        if (ch == std::char_traits<char>::eof())
+        {
+            break;
+        }
+        buf.push_back(static_cast<char>(ch));
+    }
+    return buf;
+}
+
+}  // namespace view
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END