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Walk the index of json_view through a navigation policy

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Preparation for editable documents, without a change in behavior: views and
documents get a template parameter Editable (false by default), and every
walk over the index (iterators, lookups, dump(), materialize()) goes
through detail::view::navigation<Editable>. For read-only documents it is
the plain node array, as before, so they compile without any of the edit
handling. For editable documents it also follows the representation of
edits, which this commit defines:

- node flags `edited` (a string or number token in the edit arena),
  `moved` (the elements of an array/object live in a separate sequence),
  and `is_new` (no source position), and link nodes (kind_link) that
  stand for a value stored elsewhere
- document_data::edit_state: the moved sequences, the storage of new
  values, and the edit arena

materialize() now keeps a frame per open container instead of returning
to the end of a closed one, as the serializer does, so that it can
follow moved sequences. Floats whose token lives in the edit arena (also
"nan", "inf", "-inf") are converted out of line. dump() copies only
strings of the source without escaping, and shrink_to_fit() leaves the
node array in place once there are edits, as they link into it.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-30 21:02:02 +02:00
parent eede67ca92
commit d4fab0971f
9 changed files with 484 additions and 150 deletions
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include/nlohmann/json_view.hpp
+31 -20
View File
@@ -65,7 +65,7 @@
NLOHMANN_JSON_NAMESPACE_BEGIN
template<typename BasicJsonType>
template<typename BasicJsonType, bool Editable>
class basic_json_document;
/*!
@@ -74,11 +74,13 @@ class basic_json_document;
Trivially copyable (two pointers). Valid as long as the document is alive and
has not been re-parsed, and as long as a borrowed source text is alive.
*/
template<typename BasicJsonType>
template<typename BasicJsonType, bool Editable = false>
class basic_json_view
{
using node = detail::view::node;
using document_data = detail::view::document_data;
/// how the index is walked (with edits only for editable documents)
using navigation = detail::view::navigation<Editable>;
public:
using value_t = detail::value_t;
@@ -271,7 +273,7 @@ class basic_json_view
{
detail::view::throw_type_error(305, "cannot use operator[] with a numeric argument with ", type_name());
}
return idx < m_node->len ? basic_json_view(m_doc, detail::view::element_at(m_node, idx)) : basic_json_view();
return idx < m_node->len ? basic_json_view(m_doc, navigation::value(detail::view::element_at<Editable>(*m_doc, m_node, idx))) : basic_json_view();
}
/// (an int argument would be ambiguous between size_type and const char*)
@@ -327,7 +329,7 @@ class basic_json_view
{
detail::view::throw_out_of_range(401, detail::concat("array index ", std::to_string(idx), " is out of range"));
}
return basic_json_view(m_doc, detail::view::element_at(m_node, idx));
return basic_json_view(m_doc, navigation::value(detail::view::element_at<Editable>(*m_doc, m_node, idx)));
}
basic_json_view at(int idx) const
@@ -399,7 +401,7 @@ class basic_json_view
{
if (is_structured() && m_node->len != 0)
{
return basic_json_view(m_doc, detail::view::last_child(m_node) + (is_object() ? 1 : 0));
return basic_json_view(m_doc, navigation::value(detail::view::last_child<Editable>(*m_doc, m_node) + (is_object() ? 1 : 0)));
}
return front();
}
@@ -416,7 +418,7 @@ class basic_json_view
{
return end();
}
const node* const k = detail::view::find_member(*m_doc, m_node, key.data(), key.size());
const node* const k = detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size());
return k != nullptr ? iterator(m_doc, k, true) : end();
}
@@ -433,7 +435,7 @@ class basic_json_view
/// whether this is an object with a member with this key
bool contains(string_view_t key) const
{
return is_object() && detail::view::find_member(*m_doc, m_node, key.data(), key.size()) != nullptr;
return is_object() && detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size()) != nullptr;
}
bool contains(const char* key) const
@@ -480,7 +482,7 @@ class basic_json_view
{
if (NLOHMANN_VIEW_LIKELY(is_structured()))
{
return iterator(m_doc, document_data::first_child(m_node), is_object());
return iterator(m_doc, navigation::first(*m_doc, m_node), is_object());
}
return iterator(m_doc, m_node, false);
}
@@ -489,7 +491,7 @@ class basic_json_view
{
if (NLOHMANN_VIEW_LIKELY(is_structured()))
{
return iterator(m_doc, document_data::child_end(m_node), is_object());
return iterator(m_doc, navigation::end(*m_doc, m_node), is_object());
}
return iterator(m_doc, (is_null() || is_discarded()) ? m_node : m_node + 1, false);
}
@@ -589,7 +591,7 @@ class basic_json_view
style.source_numbers = numbers == number_format::source;
// the compact text is about as long as the source text of the value
const std::size_t estimate = source_extent() + (style.pretty ? source_extent() / 2 : 0) + 64;
detail::view::view_serializer<BasicJsonType>(*m_doc, out, estimate, style).dump(m_node);
detail::view::view_serializer<BasicJsonType, Editable>(*m_doc, out, estimate, style).dump(m_node);
return out;
}
@@ -656,7 +658,7 @@ class basic_json_view
{
return BasicJsonType(value_t::discarded);
}
return detail::view::materialize<BasicJsonType>(*m_doc, m_node);
return detail::view::materialize<BasicJsonType, Editable>(*m_doc, m_node);
}
/// byte offset of this value in the source text (for strings: of the
@@ -664,12 +666,13 @@ class basic_json_view
/// a discarded view and for strings with escapes, which are decoded
std::size_t source_offset() const noexcept
{
return m_node != nullptr && (m_node->flags & detail::view::node_flags::storage) == 0
return m_node != nullptr && (m_node->flags & (detail::view::node_flags::storage | detail::view::node_flags::moved | detail::view::node_flags::is_new)) == 0
? m_node->off : static_cast<std::size_t>(-1);
}
private:
template<typename> friend class basic_json_document;
template<typename, bool> friend class basic_json_document;
template<typename, bool> friend class basic_json_view;
friend iterator;
basic_json_view(const document_data* d, const node* n) noexcept
@@ -687,6 +690,11 @@ class basic_json_view
/// decoded strings)
std::size_t source_extent() const noexcept
{
if (Editable && m_doc->edits != nullptr)
{
// positions of moved and new values are not source offsets
return m_node == m_doc->tape ? m_doc->size + m_doc->edits->text_used : 64;
}
const node* const next = document_data::after(m_node);
const bool in_source = (m_node->flags & detail::view::node_flags::storage) == 0;
if (!in_source)
@@ -704,8 +712,8 @@ class basic_json_view
/// (object required)
NLOHMANN_VIEW_ALWAYS_INLINE basic_json_view lookup(string_view_t key) const noexcept
{
const node* const k = detail::view::find_member(*m_doc, m_node, key.data(), key.size());
return k != nullptr ? basic_json_view(m_doc, k + 1) : basic_json_view();
const node* const k = detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size());
return k != nullptr ? basic_json_view(m_doc, navigation::value(k + 1)) : basic_json_view();
}
// --- get() dispatch ---
@@ -796,7 +804,7 @@ Borrowed parses keep a pointer to the caller's text, which must outlive the
document. Owned parses (parse_copy, rvalue std::string, streams, and inputs
that are not contiguous byte ranges) keep their own copy.
*/
template<typename BasicJsonType>
template<typename BasicJsonType, bool Editable = false>
class basic_json_document
{
using document_data = detail::view::document_data;
@@ -805,7 +813,7 @@ class basic_json_document
"json_view supports 64-bit integer types only");
public:
using view_type = basic_json_view<BasicJsonType>;
using view_type = basic_json_view<BasicJsonType, Editable>;
using value_t = detail::value_t;
/// an empty (discarded) document
@@ -929,7 +937,8 @@ class basic_json_document
+ (m_data->tape != m_data->inline_tape ? m_data->tape_cap * sizeof(detail::view::node) : 0)
+ m_data->arena.capacity() + m_data->owned.capacity()
+ (m_data->indexes.capacity() * sizeof(document_data::object_index)) + (m_data->index_slots.capacity() * sizeof(std::uint32_t))
+ (m_data->large_objects.capacity() * sizeof(std::uint32_t));
+ (m_data->large_objects.capacity() * sizeof(std::uint32_t))
+ (m_data->edits != nullptr ? m_data->edits->bytes : 0);
}
/// release unused capacity of the index and the decoded strings; like
@@ -948,7 +957,8 @@ class basic_json_document
// unchanged
const bool shrink_arena = d.arena.capacity() > d.arena.size();
std::string arena(shrink_arena ? d.arena : std::string());
const bool shrink_tape = d.tape != d.inline_tape && d.tape_size != d.tape_cap;
// (edits link to the nodes of the index, which then stays in place)
const bool shrink_tape = d.tape != d.inline_tape && d.tape_size != d.tape_cap && d.edits == nullptr;
const bool into_header = d.tape_size <= d.inline_cap;
node* fresh = (shrink_tape && !into_header) ? static_cast<node*>(::operator new (d.tape_size * sizeof(node))) : d.inline_tape;
@@ -998,6 +1008,8 @@ class basic_json_document
d.src = src;
d.size = size;
d.tape_size = 0;
d.edits.reset(); // (views of the previous text end here anyway)
d.base[2] = nullptr;
d.arena.clear();
d.indexes.clear();
d.index_slots.clear();
@@ -1133,7 +1145,6 @@ using json_view = basic_json_view<json>;
using ordered_json_document = basic_json_document<ordered_json>;
/// a value of an ordered_json_document
using ordered_json_view = basic_json_view<ordered_json>;
NLOHMANN_JSON_NAMESPACE_END
// tuple protocol for the items of basic_json_view::items() (structured bindings)