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Extend value to arrays when using JSON pointers (#5223)

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* ✨ extend value to arrays when using JSON pointers

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

* 💚 avoid exceptions

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

* 💚 avoid exceptions

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-07-02 06:35:35 +02:00
committed by GitHub
parent 730b57775d
commit ca49ab6123
7 changed files with 271 additions and 53 deletions
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docs/mkdocs/docs/api/basic_json/value.md
+7 -3
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@@ -94,8 +94,12 @@ changes to any JSON value.
3. The function can throw the following exceptions:
- Throws [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) if `default_value` does not match
the type of the value at `ptr`
- Throws [`type_error.306`](../../home/exceptions.md#jsonexceptiontype_error306) if the JSON value is not an object;
in that case, using `value()` with a JSON pointer makes no sense.
- Throws [`type_error.306`](../../home/exceptions.md#jsonexceptiontype_error306) if the JSON value is not an array
or object; in that case, using `value()` with a JSON pointer makes no sense.
- Throws [`parse_error.106`](../../home/exceptions.md#jsonexceptionparse_error106) if an array index in the passed
JSON pointer `ptr` begins with '0'.
- Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) if an array index in the passed
JSON pointer `ptr` is not a number.
## Complexity
@@ -180,4 +184,4 @@ changes to any JSON value.
1. Added in version 1.0.0. Changed parameter `default_value` type from `const ValueType&` to `ValueType&&` in version 3.11.0.
2. Added in version 3.11.0. Made `ValueType` the first template parameter in version 3.11.2.
3. Added in version 2.0.2.
3. Added in version 2.0.2. Extended to work with arrays in version 3.12.x.
docs/mkdocs/docs/features/element_access/default_value.md
+2 -1
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@@ -33,7 +33,8 @@ you want to access and a default value in case there is no value stored with tha
!!! failure "Exceptions"
- `value` can only be used with objects. For other types, a [`basic_json::type_error`](../../home/exceptions.md#jsonexceptiontype_error306) is thrown.
- With string keys, `value` can only be used with objects. For other types, a [`basic_json::type_error`](../../home/exceptions.md#jsonexceptiontype_error306) is thrown.
- With JSON Pointers, `value` can be used with both objects and arrays. For other types (null, boolean, number, string), a [`basic_json::type_error`](../../home/exceptions.md#jsonexceptiontype_error306) is thrown.
!!! warning "Return type"
include/nlohmann/detail/json_pointer.hpp
+92 -4
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@@ -480,8 +480,14 @@ class json_pointer
") is out of range"), ptr));
}
// note: at performs range check
ptr = &ptr->at(array_index<BasicJsonType>(reference_token));
const auto idx = array_index<BasicJsonType>(reference_token);
// Bounds check before access to avoid exception with JSON_NOEXCEPTION
if (JSON_HEDLEY_UNLIKELY(idx >= ptr->m_data.m_value.array->size()))
{
JSON_THROW(detail::out_of_range::create(401, detail::concat(
"array index ", std::to_string(idx), " is out of range"), ptr));
}
ptr = &ptr->operator[](idx);
break;
}
@@ -587,8 +593,14 @@ class json_pointer
") is out of range"), ptr));
}
// note: at performs range check
ptr = &ptr->at(array_index<BasicJsonType>(reference_token));
const auto idx = array_index<BasicJsonType>(reference_token);
// Bounds check before access to avoid exception with JSON_NOEXCEPTION
if (JSON_HEDLEY_UNLIKELY(idx >= ptr->m_data.m_value.array->size()))
{
JSON_THROW(detail::out_of_range::create(401, detail::concat(
"array index ", std::to_string(idx), " is out of range"), ptr));
}
ptr = &ptr->operator[](idx);
break;
}
@@ -608,6 +620,82 @@ class json_pointer
return *ptr;
}
/*!
@brief return a pointer to the pointed to value, or `nullptr` if the
pointer cannot be resolved because a key is missing, an array
index is out of range, or the array index is "-"
@note unlike get_checked(), this never throws for those cases, so it
can be used to implement a non-throwing fallback (e.g. value())
that also works when exceptions are disabled
@throw parse_error.106 if an array index begins with '0'
@throw parse_error.109 if an array index was not a number
*/
template<typename BasicJsonType>
const BasicJsonType* get_checked_or_null(const BasicJsonType* ptr) const
{
for (const auto& reference_token : reference_tokens)
{
switch (ptr->type())
{
case detail::value_t::object:
{
const auto it = ptr->find(reference_token);
if (JSON_HEDLEY_UNLIKELY(it == ptr->end()))
{
return nullptr;
}
ptr = &*it;
break;
}
case detail::value_t::array:
{
if (JSON_HEDLEY_UNLIKELY(reference_token == "-"))
{
// "-" always fails the range check
return nullptr;
}
// may throw parse_error.106/109 for a malformed index; an
// index that is syntactically valid but cannot be
// represented (out_of_range.404/410) is treated like an
// out-of-range index below
typename BasicJsonType::size_type idx{};
JSON_TRY
{
idx = array_index<BasicJsonType>(reference_token);
}
JSON_INTERNAL_CATCH (detail::out_of_range&)
{
return nullptr;
}
if (JSON_HEDLEY_UNLIKELY(idx >= ptr->m_data.m_value.array->size()))
{
return nullptr;
}
ptr = &ptr->operator[](idx);
break;
}
case detail::value_t::null:
case detail::value_t::string:
case detail::value_t::boolean:
case detail::value_t::number_integer:
case detail::value_t::number_unsigned:
case detail::value_t::number_float:
case detail::value_t::binary:
case detail::value_t::discarded:
default:
return nullptr;
}
}
return ptr;
}
/*!
@throw parse_error.106 if an array index begins with '0'
@throw parse_error.109 if an array index was not a number
include/nlohmann/json.hpp
+14 -16
View File
@@ -2393,19 +2393,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
&& !std::is_same<value_t, detail::uncvref_t<ValueType>>::value, int > = 0 >
ValueType value(const json_pointer& ptr, const ValueType& default_value) const
{
// value only works for objects
if (JSON_HEDLEY_LIKELY(is_object()))
// value only works for arrays and objects
if (JSON_HEDLEY_LIKELY(is_structured()))
{
// If the pointer resolves to a value, return it. Otherwise, return
// 'default_value'.
JSON_TRY
const auto* res = ptr.get_checked_or_null(this);
if (JSON_HEDLEY_LIKELY(res != nullptr))
{
return ptr.get_checked(this).template get<ValueType>();
}
JSON_INTERNAL_CATCH (out_of_range&)
{
return default_value;
return res->template get<ValueType>();
}
return default_value;
}
JSON_THROW(type_error::create(306, detail::concat("cannot use value() with ", type_name()), this));
@@ -2419,19 +2418,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
&& !std::is_same<value_t, detail::uncvref_t<ValueType>>::value, int > = 0 >
ReturnType value(const json_pointer& ptr, ValueType && default_value) const
{
// value only works for objects
if (JSON_HEDLEY_LIKELY(is_object()))
// value only works for arrays and objects
if (JSON_HEDLEY_LIKELY(is_structured()))
{
// If the pointer resolves to a value, return it. Otherwise, return
// 'default_value'.
JSON_TRY
const auto* res = ptr.get_checked_or_null(this);
if (JSON_HEDLEY_LIKELY(res != nullptr))
{
return ptr.get_checked(this).template get<ReturnType>();
}
JSON_INTERNAL_CATCH (out_of_range&)
{
return std::forward<ValueType>(default_value);
return res->template get<ReturnType>();
}
return std::forward<ValueType>(default_value);
}
JSON_THROW(type_error::create(306, detail::concat("cannot use value() with ", type_name()), this));
single_include/nlohmann/json.hpp
+106 -20
View File
@@ -15401,8 +15401,14 @@ class json_pointer
") is out of range"), ptr));
}
// note: at performs range check
ptr = &ptr->at(array_index<BasicJsonType>(reference_token));
const auto idx = array_index<BasicJsonType>(reference_token);
// Bounds check before access to avoid exception with JSON_NOEXCEPTION
if (JSON_HEDLEY_UNLIKELY(idx >= ptr->m_data.m_value.array->size()))
{
JSON_THROW(detail::out_of_range::create(401, detail::concat(
"array index ", std::to_string(idx), " is out of range"), ptr));
}
ptr = &ptr->operator[](idx);
break;
}
@@ -15508,8 +15514,14 @@ class json_pointer
") is out of range"), ptr));
}
// note: at performs range check
ptr = &ptr->at(array_index<BasicJsonType>(reference_token));
const auto idx = array_index<BasicJsonType>(reference_token);
// Bounds check before access to avoid exception with JSON_NOEXCEPTION
if (JSON_HEDLEY_UNLIKELY(idx >= ptr->m_data.m_value.array->size()))
{
JSON_THROW(detail::out_of_range::create(401, detail::concat(
"array index ", std::to_string(idx), " is out of range"), ptr));
}
ptr = &ptr->operator[](idx);
break;
}
@@ -15529,6 +15541,82 @@ class json_pointer
return *ptr;
}
/*!
@brief return a pointer to the pointed to value, or `nullptr` if the
pointer cannot be resolved because a key is missing, an array
index is out of range, or the array index is "-"
@note unlike get_checked(), this never throws for those cases, so it
can be used to implement a non-throwing fallback (e.g. value())
that also works when exceptions are disabled
@throw parse_error.106 if an array index begins with '0'
@throw parse_error.109 if an array index was not a number
*/
template<typename BasicJsonType>
const BasicJsonType* get_checked_or_null(const BasicJsonType* ptr) const
{
for (const auto& reference_token : reference_tokens)
{
switch (ptr->type())
{
case detail::value_t::object:
{
const auto it = ptr->find(reference_token);
if (JSON_HEDLEY_UNLIKELY(it == ptr->end()))
{
return nullptr;
}
ptr = &*it;
break;
}
case detail::value_t::array:
{
if (JSON_HEDLEY_UNLIKELY(reference_token == "-"))
{
// "-" always fails the range check
return nullptr;
}
// may throw parse_error.106/109 for a malformed index; an
// index that is syntactically valid but cannot be
// represented (out_of_range.404/410) is treated like an
// out-of-range index below
typename BasicJsonType::size_type idx{};
JSON_TRY
{
idx = array_index<BasicJsonType>(reference_token);
}
JSON_INTERNAL_CATCH (detail::out_of_range&)
{
return nullptr;
}
if (JSON_HEDLEY_UNLIKELY(idx >= ptr->m_data.m_value.array->size()))
{
return nullptr;
}
ptr = &ptr->operator[](idx);
break;
}
case detail::value_t::null:
case detail::value_t::string:
case detail::value_t::boolean:
case detail::value_t::number_integer:
case detail::value_t::number_unsigned:
case detail::value_t::number_float:
case detail::value_t::binary:
case detail::value_t::discarded:
default:
return nullptr;
}
}
return ptr;
}
/*!
@throw parse_error.106 if an array index begins with '0'
@throw parse_error.109 if an array index was not a number
@@ -22911,19 +22999,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
&& !std::is_same<value_t, detail::uncvref_t<ValueType>>::value, int > = 0 >
ValueType value(const json_pointer& ptr, const ValueType& default_value) const
{
// value only works for objects
if (JSON_HEDLEY_LIKELY(is_object()))
// value only works for arrays and objects
if (JSON_HEDLEY_LIKELY(is_structured()))
{
// If the pointer resolves to a value, return it. Otherwise, return
// 'default_value'.
JSON_TRY
const auto* res = ptr.get_checked_or_null(this);
if (JSON_HEDLEY_LIKELY(res != nullptr))
{
return ptr.get_checked(this).template get<ValueType>();
}
JSON_INTERNAL_CATCH (out_of_range&)
{
return default_value;
return res->template get<ValueType>();
}
return default_value;
}
JSON_THROW(type_error::create(306, detail::concat("cannot use value() with ", type_name()), this));
@@ -22937,19 +23024,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
&& !std::is_same<value_t, detail::uncvref_t<ValueType>>::value, int > = 0 >
ReturnType value(const json_pointer& ptr, ValueType && default_value) const
{
// value only works for objects
if (JSON_HEDLEY_LIKELY(is_object()))
// value only works for arrays and objects
if (JSON_HEDLEY_LIKELY(is_structured()))
{
// If the pointer resolves to a value, return it. Otherwise, return
// 'default_value'.
JSON_TRY
const auto* res = ptr.get_checked_or_null(this);
if (JSON_HEDLEY_LIKELY(res != nullptr))
{
return ptr.get_checked(this).template get<ReturnType>();
}
JSON_INTERNAL_CATCH (out_of_range&)
{
return std::forward<ValueType>(default_value);
return res->template get<ReturnType>();
}
return std::forward<ValueType>(default_value);
}
JSON_THROW(type_error::create(306, detail::concat("cannot use value() with ", type_name()), this));
tests/module_cpp20/main.cpp
+1 -1
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@@ -55,5 +55,5 @@ int main()
// use every result so the references cannot be optimized away
return (a == 1 && last == 3 && b == 2 && lit.size() == 3
&& m.size() == 1 && !dumped.empty() && !os.str().empty())
? 0 : 1;
? 0 : 1;
}
tests/src/unit-element_access2.cpp
+49 -8
View File
@@ -419,14 +419,6 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
CHECK_THROWS_WITH_AS(j_nonobject_const.value("/foo"_json_pointer, 1), "[json.exception.type_error.306] cannot use value() with string", typename Json::type_error&);
}
SECTION("array")
{
Json j_nonobject(Json::value_t::array);
const Json j_nonobject_const(Json::value_t::array);
CHECK_THROWS_WITH_AS(j_nonobject.value("/foo"_json_pointer, 1), "[json.exception.type_error.306] cannot use value() with array", typename Json::type_error&);
CHECK_THROWS_WITH_AS(j_nonobject_const.value("/foo"_json_pointer, 1), "[json.exception.type_error.306] cannot use value() with array", typename Json::type_error&);
}
SECTION("number (integer)")
{
Json j_nonobject(Json::value_t::number_integer);
@@ -451,6 +443,55 @@ TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_j
CHECK_THROWS_WITH_AS(j_nonobject_const.value("/foo"_json_pointer, 1), "[json.exception.type_error.306] cannot use value() with number", typename Json::type_error&);
}
}
SECTION("access on array type")
{
Json j_array = Json::array({j});
const Json j_array_const = Json::array({j});
CHECK(j_array.value("/0/integer"_json_pointer, 2) == 1);
CHECK(j_array.value("/0/integer"_json_pointer, 1.0) == Approx(1));
CHECK(j_array.value("/0/unsigned"_json_pointer, 2) == 1u);
CHECK(j_array.value("/0/unsigned"_json_pointer, 1.0) == Approx(1u));
CHECK(j_array.value("/0/null"_json_pointer, Json(1)) == Json());
CHECK(j_array.value("/0/boolean"_json_pointer, false) == true);
CHECK(j_array.value("/0/string"_json_pointer, "bar") == "hello world");
CHECK(j_array.value("/0/string"_json_pointer, std::string("bar")) == "hello world");
CHECK(j_array.value("/0/floating"_json_pointer, 12.34) == Approx(42.23));
CHECK(j_array.value("/0/floating"_json_pointer, 12) == 42);
CHECK(j_array.value("/0/object"_json_pointer, Json({{"foo", "bar"}})) == Json::object());
CHECK(j_array.value("/0/array"_json_pointer, Json({10, 100})) == Json({1, 2, 3}));
CHECK(j_array_const.value("/0/integer"_json_pointer, 2) == 1);
CHECK(j_array_const.value("/0/integer"_json_pointer, 1.0) == Approx(1));
CHECK(j_array_const.value("/0/unsigned"_json_pointer, 2) == 1u);
CHECK(j_array_const.value("/0/unsigned"_json_pointer, 1.0) == Approx(1u));
CHECK(j_array_const.value("/0/boolean"_json_pointer, false) == true);
CHECK(j_array_const.value("/0/string"_json_pointer, "bar") == "hello world");
CHECK(j_array_const.value("/0/string"_json_pointer, std::string("bar")) == "hello world");
CHECK(j_array_const.value("/0/floating"_json_pointer, 12.34) == Approx(42.23));
CHECK(j_array_const.value("/0/floating"_json_pointer, 12) == 42);
CHECK(j_array_const.value("/0/object"_json_pointer, Json({{"foo", "bar"}})) == Json::object());
CHECK(j_array_const.value("/0/array"_json_pointer, Json({10, 100})) == Json({1, 2, 3}));
// Test out-of-range array index
CHECK(j_array.value("/10"_json_pointer, 42) == 42);
CHECK(j_array_const.value("/10"_json_pointer, 42) == 42);
// Test "-" index (append position is invalid)
CHECK(j_array.value("/-"_json_pointer, 42) == 42);
CHECK(j_array_const.value("/-"_json_pointer, 42) == 42);
#if !defined(JSON_NOEXCEPTION)
// Test malformed index (non-numeric) throws parse_error
CHECK_THROWS_WITH_AS(j_array.value("/foo"_json_pointer, 1), "[json.exception.parse_error.109] parse error: array index 'foo' is not a number", typename Json::parse_error&);
CHECK_THROWS_WITH_AS(j_array_const.value("/foo"_json_pointer, 1), "[json.exception.parse_error.109] parse error: array index 'foo' is not a number", typename Json::parse_error&);
// Test leading-zero index throws parse_error
CHECK_THROWS_WITH_AS(j_array.value("/01"_json_pointer, 1), "[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'", typename Json::parse_error&);
CHECK_THROWS_WITH_AS(j_array_const.value("/01"_json_pointer, 1), "[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'", typename Json::parse_error&);
#endif
}
}
}