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json_view: view_mode enum instead of bool Editable, node_kind for node::kind (#5919)

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* json_view: view_mode enum instead of bool Editable, node_kind for node::kind

basic_json_document and basic_json_view take a view_mode (read_only, the
default, or editable) instead of a bool: basic_json_document<json, true>
did not say what true means. The shortcut aliases are unchanged.

The kind of a node is a node_kind (the value_t values plus link, 10 as
before), which removes the static_cast<std::uint8_t>(value_t::...) of
every comparison. The node and image layouts are unchanged.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* json_view: node_kind in the node writers, spell out read_only, comment fixes

The builder and the edit functions take and store a node_kind instead of
casting a value_t; the numbering assertions and the comments now speak of
node_kind, and the link kind notes that it follows value_t::discarded.
The read-only aliases name view_mode::read_only like the editable ones.
view_mode.md says the mode is a compile-time property of the type.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* json_view: views of read-only documents convert to editable views

A read-only document has no edits, so a view of it reads correctly as a
view of an editable document before its first edit. The implicit
conversion lets a function taking a json_editable_view accept the views
of both modes. There is no conversion the other way: a read-only view of
an editable document would read wrong values after the next edit.

The mode comparisons in the cross-mode operator==/!= use an
is_other_mode trait, which astyle keeps compact.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann authored and GitHub committed 2026-10-26 20:13:30 +01:00
1 parent 24078c862d
commit 731f1b5bfb
38 files changed
+704 -293
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include/nlohmann/json_view.hpp
+45 -29
View File
@@ -84,6 +84,7 @@
#include <nlohmann/detail/view/serializer.hpp>
#include <nlohmann/detail/view/string_ref.hpp>
#include <nlohmann/detail/view/value.hpp>
#include <nlohmann/detail/view/view_mode.hpp>
NLOHMANN_JSON_NAMESPACE_BEGIN
@@ -93,13 +94,16 @@ NLOHMANN_JSON_NAMESPACE_BEGIN
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, bool Editable = false>
template<typename BasicJsonType, view_mode Mode = view_mode::read_only>
class basic_json_view
{
/// whether this is a view of an editable document
static constexpr bool is_editable = Mode == view_mode::editable;
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>;
using navigation = detail::view::navigation<is_editable>;
public:
using value_t = detail::value_t;
@@ -120,6 +124,15 @@ class basic_json_view
/// an invalid view (type() == value_t::discarded)
basic_json_view() noexcept = default;
/// a view of a read-only document as a view of an editable one, so that a
/// function taking an editable view accepts both (a read-only document has
/// no edits; the view reads it as an editable document before its first
/// edit, at the cost of one check per access)
template<view_mode M, detail::enable_if_t<detail::view::is_widening_mode<M, Mode>::value, int> = 0>
basic_json_view(const basic_json_view<BasicJsonType, M>& other) noexcept // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
: m_doc(other.m_doc), m_node(other.m_node)
{}
//////////
// type //
//////////
@@ -446,7 +459,7 @@ class basic_json_view
if (is_structured() && m_node->len != 0)
{
return unedited() ? basic_json_view(m_doc, detail::view::last_child<false>(*m_doc, m_node) + (is_object() ? 1 : 0))
: basic_json_view(m_doc, navigation::value(detail::view::last_child<Editable>(*m_doc, m_node) + (is_object() ? 1 : 0)));
: basic_json_view(m_doc, navigation::value(detail::view::last_child<is_editable>(*m_doc, m_node) + (is_object() ? 1 : 0)));
}
return front();
}
@@ -504,7 +517,7 @@ class basic_json_view
/// more than once); 0 if this is not an object
size_type count(string_view_t key) const
{
return is_object() ? detail::view::count_members<Editable>(*m_doc, m_node, key.data(), key.size()) : 0;
return is_object() ? detail::view::count_members<is_editable>(*m_doc, m_node, key.data(), key.size()) : 0;
}
size_type count(const char* key) const
@@ -646,7 +659,7 @@ class basic_json_view
}
else
{
detail::view::view_serializer<BasicJsonType, Editable>(*m_doc, out, estimate, style).dump(m_node);
detail::view::view_serializer<BasicJsonType, is_editable>(*m_doc, out, estimate, style).dump(m_node);
}
return out;
}
@@ -682,14 +695,14 @@ class basic_json_view
}
/// a view of an editable document compares with one of a read-only document
template < bool E, typename std::enable_if < E != Editable, int >::type = 0 >
friend bool operator==(const basic_json_view& a, const basic_json_view<BasicJsonType, E>& b)
template<view_mode M, detail::enable_if_t<detail::view::is_other_mode<M, Mode>::value, int> = 0>
friend bool operator==(const basic_json_view& a, const basic_json_view<BasicJsonType, M>& b)
{
return detail::view::equal<BasicJsonType>(side(a), detail::view::view_side<BasicJsonType, basic_json_view<BasicJsonType, E>>(b));
return detail::view::equal<BasicJsonType>(side(a), detail::view::view_side<BasicJsonType, basic_json_view<BasicJsonType, M>>(b));
}
template < bool E, typename std::enable_if < E != Editable, int >::type = 0 >
friend bool operator!=(const basic_json_view& a, const basic_json_view<BasicJsonType, E>& b)
template<view_mode M, detail::enable_if_t<detail::view::is_other_mode<M, Mode>::value, int> = 0>
friend bool operator!=(const basic_json_view& a, const basic_json_view<BasicJsonType, M>& b)
{
return !(a == b);
}
@@ -727,7 +740,7 @@ class basic_json_view
{
return BasicJsonType(value_t::discarded);
}
return unedited() ? detail::view::materialize<BasicJsonType, false>(*m_doc, m_node) : detail::view::materialize<BasicJsonType, Editable>(*m_doc, m_node);
return unedited() ? detail::view::materialize<BasicJsonType, false>(*m_doc, m_node) : detail::view::materialize<BasicJsonType, is_editable>(*m_doc, m_node);
}
/// byte offset of this value in the source text (for strings: of the
@@ -740,8 +753,8 @@ class basic_json_view
}
private:
template<typename, bool> friend class basic_json_document;
template<typename, bool> friend class basic_json_view;
template<typename, view_mode> friend class basic_json_document;
template<typename, view_mode> friend class basic_json_view;
template<typename, typename> friend class detail::view::editor;
friend iterator;
@@ -757,11 +770,11 @@ class basic_json_view
}
/// the template argument as a runtime condition: testing it directly in
/// `Editable && ...` makes the condition constant, which MSVC reports as
/// `is_editable && ...` makes the condition constant, which MSVC reports as
/// C4127
static bool editable() noexcept
{
return Editable;
return is_editable;
}
/// the number of source bytes of this value (estimated for values with
@@ -810,7 +823,7 @@ class basic_json_view
const node* const k = detail::view::find_member<false>(*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());
const node* const k = detail::view::find_member<is_editable>(*m_doc, m_node, key.data(), key.size());
return k != nullptr ? basic_json_view(m_doc, navigation::value(k + 1)) : basic_json_view();
}
@@ -824,7 +837,7 @@ class basic_json_view
/// the member of this object with @a key (the last one if the key occurs more than once), or nullptr
NLOHMANN_VIEW_ALWAYS_INLINE const node* find_key(string_view_t key) const
{
return find_key(key, std::integral_constant<bool, Editable> {});
return find_key(key, std::integral_constant<bool, is_editable> {});
}
NLOHMANN_VIEW_ALWAYS_INLINE const node* find_key(string_view_t key, std::true_type /*editable*/) const
@@ -846,7 +859,7 @@ class basic_json_view
{
return basic_json_view(m_doc, detail::view::element_at<false>(*m_doc, m_node, idx));
}
return basic_json_view(m_doc, navigation::value(detail::view::element_at<Editable>(*m_doc, m_node, idx)));
return basic_json_view(m_doc, navigation::value(detail::view::element_at<is_editable>(*m_doc, m_node, idx)));
}
// --- get() dispatch ---
@@ -952,16 +965,19 @@ 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, bool Editable = false>
template<typename BasicJsonType, view_mode Mode = view_mode::read_only>
class basic_json_document
{
/// whether the document can be edited
static constexpr bool is_editable = Mode == view_mode::editable;
using document_data = detail::view::document_data;
static_assert(sizeof(typename BasicJsonType::number_integer_t) == 8 && sizeof(typename BasicJsonType::number_unsigned_t) == 8,
"json_view supports 64-bit integer types only");
public:
using view_type = basic_json_view<BasicJsonType, Editable>;
using view_type = basic_json_view<BasicJsonType, Mode>;
using value_t = detail::value_t;
/// an empty (discarded) document
@@ -1357,7 +1373,7 @@ class basic_json_document
detail::view::editor<BasicJsonType, view_type> editor()
{
static_assert(Editable, "only an editable document can be edited: use basic_json_document<BasicJsonType, true> (json_editable_document)");
static_assert(is_editable, "only an editable document can be edited: use basic_json_document<BasicJsonType, view_mode::editable> (json_editable_document)");
if (NLOHMANN_VIEW_UNLIKELY(!m_data || m_data->discarded))
{
detail::view::throw_invalid_iterator(detail::exception_id::iterator_from_other_value, "view does not belong to this document");
@@ -1634,21 +1650,21 @@ class basic_json_document
};
/// a parsed JSON text for json
using json_document = basic_json_document<json>;
using json_document = basic_json_document<json, view_mode::read_only>;
/// a value of a json_document
using json_view = basic_json_view<json>;
using json_view = basic_json_view<json, view_mode::read_only>;
/// a parsed JSON text for ordered_json
using ordered_json_document = basic_json_document<ordered_json>;
using ordered_json_document = basic_json_document<ordered_json, view_mode::read_only>;
/// a value of an ordered_json_document
using ordered_json_view = basic_json_view<ordered_json>;
using ordered_json_view = basic_json_view<ordered_json, view_mode::read_only>;
/// an editable parsed JSON text for json
using json_editable_document = basic_json_document<json, true>;
using json_editable_document = basic_json_document<json, view_mode::editable>;
/// a value of a json_editable_document
using json_editable_view = basic_json_view<json, true>;
using json_editable_view = basic_json_view<json, view_mode::editable>;
/// an editable parsed JSON text for ordered_json
using ordered_json_editable_document = basic_json_document<ordered_json, true>;
using ordered_json_editable_document = basic_json_document<ordered_json, view_mode::editable>;
/// a value of an ordered_json_editable_document
using ordered_json_editable_view = basic_json_view<ordered_json, true>;
using ordered_json_editable_view = basic_json_view<ordered_json, view_mode::editable>;
NLOHMANN_JSON_NAMESPACE_END