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re-adding const version operator[] (#135, #159)
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It was a good idea to implement a const version of operator[] it in the
first place. I was a pity that this implementation was flawed. It was a
mistake to remove the const version completely. This commit
re-introduces the const version. My apologies for all the inconvenience.
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@nlohmann
nlohmann committed Dec 21, 2015
1 parent 9def018 commit 4351698
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Showing 5 changed files with 197 additions and 2 deletions.
2 changes: 1 addition & 1 deletion doc/examples/operatorarray__key_type_const.cpp
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Expand Up @@ -5,7 +5,7 @@ using namespace nlohmann;
int main()
{
// create a JSON object
json object =
const json object =
{
{"one", 1}, {"two", 2}, {"three", 2.9}
};
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2 changes: 1 addition & 1 deletion doc/examples/operatorarray__key_type_const.link
View file
@@ -1 +1 @@
<a target="_blank" href="http://melpon.org/wandbox/permlink/9X5Q8p7DlWA6v0Ey"><b>online</b></a>
<a target="_blank" href="http://melpon.org/wandbox/permlink/4WLxv7id8P64Q1KI"><b>online</b></a>
81 changes: 81 additions & 0 deletions src/json.hpp
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Expand Up @@ -2862,6 +2862,45 @@ class basic_json
}
}

/*!
@brief read-only access specified object element
Returns a const reference to the element at with specified key @a key. No
bounds checking is performed.
@warning If the element with key @a key does not exist, the behavior is
undefined.
@param[in] key key of the element to access
@return const reference to the element at key @a key
@throw std::domain_error if JSON is not an object
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read using
the [] operator.,operatorarray__key_type_const}
@sa @ref at(const typename object_t::key_type&) for access by reference
with range checking
@sa @ref value() for access by value with a default value
@since version 1.0
*/
const_reference operator[](const typename object_t::key_type& key) const
{
// [] only works for objects
if (is_object())
{
return m_value.object->find(key)->second;
}
else
{
throw std::domain_error("cannot use operator[] with " + type_name());
}
}

/*!
@brief access specified object element
Expand Down Expand Up @@ -2911,6 +2950,48 @@ class basic_json
}
}

/*!
@brief read-only access specified object element
Returns a const reference to the element at with specified key @a key. No
bounds checking is performed.
@warning If the element with key @a key does not exist, the behavior is
undefined.
@note This function is required for compatibility reasons with Clang.
@param[in] key key of the element to access
@return const reference to the element at key @a key
@throw std::domain_error if JSON is not an object
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read using
the [] operator.,operatorarray__key_type_const}
@sa @ref at(const typename object_t::key_type&) for access by reference
with range checking
@sa @ref value() for access by value with a default value
@since version 1.0
*/
template<typename T, std::size_t n>
const_reference operator[](const T (&key)[n]) const
{
// at only works for objects
if (is_object())
{
return m_value.object->find(key)->second;
}
else
{
throw std::domain_error("cannot use operator[] with " + type_name());
}
}

/*!
@brief access specified object element with default value
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81 changes: 81 additions & 0 deletions src/json.hpp.re2c
View file
Expand Up @@ -2862,6 +2862,45 @@ class basic_json
}
}

/*!
@brief read-only access specified object element

Returns a const reference to the element at with specified key @a key. No
bounds checking is performed.

@warning If the element with key @a key does not exist, the behavior is
undefined.

@param[in] key key of the element to access

@return const reference to the element at key @a key

@throw std::domain_error if JSON is not an object

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read using
the [] operator.,operatorarray__key_type_const}

@sa @ref at(const typename object_t::key_type&) for access by reference
with range checking
@sa @ref value() for access by value with a default value

@since version 1.0
*/
const_reference operator[](const typename object_t::key_type& key) const
{
// [] only works for objects
if (is_object())
{
return m_value.object->find(key)->second;
}
else
{
throw std::domain_error("cannot use operator[] with " + type_name());
}
}

/*!
@brief access specified object element

Expand Down Expand Up @@ -2911,6 +2950,48 @@ class basic_json
}
}

/*!
@brief read-only access specified object element

Returns a const reference to the element at with specified key @a key. No
bounds checking is performed.

@warning If the element with key @a key does not exist, the behavior is
undefined.

@note This function is required for compatibility reasons with Clang.

@param[in] key key of the element to access

@return const reference to the element at key @a key

@throw std::domain_error if JSON is not an object

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read using
the [] operator.,operatorarray__key_type_const}

@sa @ref at(const typename object_t::key_type&) for access by reference
with range checking
@sa @ref value() for access by value with a default value

@since version 1.0
*/
template<typename T, std::size_t n>
const_reference operator[](const T (&key)[n]) const
{
// at only works for objects
if (is_object())
{
return m_value.object->find(key)->second;
}
else
{
throw std::domain_error("cannot use operator[] with " + type_name());
}
}

/*!
@brief access specified object element with default value

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33 changes: 33 additions & 0 deletions test/unit.cpp
View file
Expand Up @@ -3211,6 +3211,27 @@ TEST_CASE("element access")

CHECK(j["array"] == json({1, 2, 3}));
CHECK(j[json::object_t::key_type("array")] == j["array"]);

CHECK(j_const["integer"] == json(1));
CHECK(j_const[json::object_t::key_type("integer")] == j["integer"]);

CHECK(j_const["boolean"] == json(true));
CHECK(j_const[json::object_t::key_type("boolean")] == j["boolean"]);

CHECK(j_const["null"] == json(nullptr));
CHECK(j_const[json::object_t::key_type("null")] == j["null"]);

CHECK(j_const["string"] == json("hello world"));
CHECK(j_const[json::object_t::key_type("string")] == j["string"]);

CHECK(j_const["floating"] == json(42.23));
CHECK(j_const[json::object_t::key_type("floating")] == j["floating"]);

CHECK(j_const["object"] == json(json::object()));
CHECK(j_const[json::object_t::key_type("object")] == j["object"]);

CHECK(j_const["array"] == json({1, 2, 3}));
CHECK(j_const[json::object_t::key_type("array")] == j["array"]);
}

SECTION("access on non-object type")
Expand All @@ -3222,6 +3243,8 @@ TEST_CASE("element access")
const json j_const_nonobject(j_nonobject);
CHECK_NOTHROW(j_nonobject["foo"]);
CHECK_NOTHROW(j_nonobject2[json::object_t::key_type("foo")]);
CHECK_THROWS_AS(j_const_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject[json::object_t::key_type("foo")], std::domain_error);
}

SECTION("boolean")
Expand All @@ -3230,6 +3253,8 @@ TEST_CASE("element access")
const json j_const_nonobject(j_nonobject);
CHECK_THROWS_AS(j_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_nonobject[json::object_t::key_type("foo")], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject[json::object_t::key_type("foo")], std::domain_error);
}

SECTION("string")
Expand All @@ -3238,6 +3263,8 @@ TEST_CASE("element access")
const json j_const_nonobject(j_nonobject);
CHECK_THROWS_AS(j_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_nonobject[json::object_t::key_type("foo")], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject[json::object_t::key_type("foo")], std::domain_error);
}

SECTION("array")
Expand All @@ -3246,6 +3273,8 @@ TEST_CASE("element access")
const json j_const_nonobject(j_nonobject);
CHECK_THROWS_AS(j_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_nonobject[json::object_t::key_type("foo")], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject[json::object_t::key_type("foo")], std::domain_error);
}

SECTION("number (integer)")
Expand All @@ -3254,6 +3283,8 @@ TEST_CASE("element access")
const json j_const_nonobject(j_nonobject);
CHECK_THROWS_AS(j_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_nonobject[json::object_t::key_type("foo")], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject[json::object_t::key_type("foo")], std::domain_error);
}

SECTION("number (floating-point)")
Expand All @@ -3262,6 +3293,8 @@ TEST_CASE("element access")
const json j_const_nonobject(j_nonobject);
CHECK_THROWS_AS(j_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_nonobject[json::object_t::key_type("foo")], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject["foo"], std::domain_error);
CHECK_THROWS_AS(j_const_nonobject[json::object_t::key_type("foo")], std::domain_error);
}
}
}
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