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Commit bd2783f4 by dariomt
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Added get_ref()

Same as get_ptr() but for references. If the type is incompatible it throws (get_ptr() returns null). Implemented in terms of get_ptr().
parent 8f97e99f
Showing with 273 additions and 2 deletions
doc/examples/get_ref.cpp 0 → 100644
#include <json.hpp>
using namespace nlohmann;
int main()
{
// create a JSON number
json value = 17;
// explicitly getting references
auto r1 = value.get_ref<const json::number_integer_t&>();
auto r2 = value.get_ref<json::number_integer_t&>();
// print the values
std::cout << r1 << ' ' << r2 << '\n';
// incompatible type throws exception
try
{
auto r3 = value.get_ref<json::number_float_t&>();
}
catch(std::domain_error& ex)
{
std::cout << ex.what() << '\n';
}
}
src/json.hpp
......@@ -2251,6 +2251,19 @@ class basic_json
return is_number_float() ? &m_value.number_float : nullptr;
}
/// helper function to implement get_ref without code duplication
/// for const and non-const overloads
/// ThisType will be deduced as 'basic_jason' or 'const basic_json'
template<typename ReferenceType, typename ThisType>
static ReferenceType get_ref_impl(ThisType& obj)
{
using PointerType = std::add_pointer<ReferenceType>::type;
// delegate the call to get_ptr<>()
auto ptr = obj.get_ptr<PointerType>();
if (ptr) return *ptr;
throw std::domain_error("incompatible ReferenceType for get_ref, actual type is " + obj.type_name());
}
public:
/// @name value access
......@@ -2387,10 +2400,56 @@ class basic_json
std::is_pointer<PointerType>::value
and std::is_const< typename std::remove_pointer<PointerType>::type >::value
, int>::type = 0>
const PointerType get_ptr() const noexcept
PointerType get_ptr() const noexcept
{
// delegate the call to get_impl_ptr<>() const
return get_impl_ptr(static_cast<const PointerType>(nullptr));
return get_impl_ptr(static_cast<PointerType>(nullptr));
}
/*!
@brief get a reference value (implicit)
Implict reference access to the internally stored JSON value. No copies are
made.
@warning Writing data to the referee of the result yields an undefined
state.
@tparam ReferenceType reference type; must be a reference to @ref array_t, @ref
object_t, @ref string_t, @ref boolean_t, @ref number_integer_t, or @ref
number_float_t.
@return reference to the internally stored JSON value if the requested reference
type @a ReferenceType fits to the JSON value; throws std::domain_error otherwise
@throw std::domain_error in case passed type @a ReferenceType is incompatible
with the stored JSON value
@complexity Constant.
*/
template<typename ReferenceType, typename
std::enable_if<
std::is_reference<ReferenceType>::value
, int>::type = 0>
ReferenceType get_ref()
{
// delegate call to get_ref_impl
return get_ref_impl<ReferenceType>(*this);
}
/*!
@brief get a reference value (implicit)
@copydoc get_ref()
*/
template<typename ReferenceType, typename
std::enable_if<
std::is_reference<ReferenceType>::value
and std::is_const< typename std::remove_reference<ReferenceType>::type >::value
, int>::type = 0>
ReferenceType get_ref() const
{
// delegate call to get_ref_impl
return get_ref_impl<ReferenceType>(*this);
}
/*!
......
test/unit.cpp
......@@ -2494,6 +2494,22 @@ TEST_CASE("pointer access")
CHECK(value.get_ptr<json::number_float_t*>() == nullptr);
}
SECTION("pointer access to const object_t")
{
using test_type = json::object_t;
const json value = {{"one", 1}, {"two", 2}};
// this should not compile
// test_type* p1 = value.get_ptr<test_type*>();
// check if pointers are returned correctly
const test_type* p2 = value.get_ptr<const test_type*>();
CHECK(*p2 == value.get<test_type>());
const test_type* const p3 = value.get_ptr<const test_type* const>();
CHECK(p2 == p3);
}
SECTION("pointer access to array_t")
{
using test_type = json::array_t;
......@@ -2630,6 +2646,176 @@ TEST_CASE("pointer access")
}
}
TEST_CASE("reference access")
{
// create a JSON value with different types
json json_types =
{
{"boolean", true},
{
"number", {
{"integer", 42},
{"floating-point", 17.23}
}
},
{"string", "Hello, world!"},
{"array", {1, 2, 3, 4, 5}},
{"null", nullptr}
};
SECTION("reference access to object_t")
{
using test_type = json::object_t;
json value = {{"one", 1}, {"two", 2}};
// check if references are returned correctly
test_type& p1 = value.get_ref<test_type&>();
CHECK(&p1 == value.get_ptr<test_type*>());
CHECK(p1 == value.get<test_type>());
const test_type& p2 = value.get_ref<const test_type&>();
CHECK(&p2 == value.get_ptr<const test_type*>());
CHECK(p2 == value.get<test_type>());
// check if mismatching references throw correctly
CHECK_NOTHROW(value.get_ref<json::object_t&>());
CHECK_THROWS(value.get_ref<json::array_t&>());
CHECK_THROWS(value.get_ref<json::string_t&>());
CHECK_THROWS(value.get_ref<json::boolean_t&>());
CHECK_THROWS(value.get_ref<json::number_integer_t&>());
CHECK_THROWS(value.get_ref<json::number_float_t&>());
}
SECTION("const reference access to const object_t")
{
using test_type = json::object_t;
const json value = {{"one", 1}, {"two", 2}};
// this should not compile
// test_type& p1 = value.get_ref<test_type&>();
// check if references are returned correctly
const test_type& p2 = value.get_ref<const test_type&>();
CHECK(&p2 == value.get_ptr<const test_type*>());
CHECK(p2 == value.get<test_type>());
}
SECTION("reference access to array_t")
{
using test_type = json::array_t;
json value = {1, 2, 3, 4};
// check if references are returned correctly
test_type& p1 = value.get_ref<test_type&>();
CHECK(&p1 == value.get_ptr<test_type*>());
CHECK(p1 == value.get<test_type>());
const test_type& p2 = value.get_ref<const test_type&>();
CHECK(&p2 == value.get_ptr<const test_type*>());
CHECK(p2 == value.get<test_type>());
// check if mismatching references throw correctly
CHECK_THROWS(value.get_ref<json::object_t&>());
CHECK_NOTHROW(value.get_ref<json::array_t&>());
CHECK_THROWS(value.get_ref<json::string_t&>());
CHECK_THROWS(value.get_ref<json::boolean_t&>());
CHECK_THROWS(value.get_ref<json::number_integer_t&>());
CHECK_THROWS(value.get_ref<json::number_float_t&>());
}
SECTION("reference access to string_t")
{
using test_type = json::string_t;
json value = "hello";
// check if references are returned correctly
test_type& p1 = value.get_ref<test_type&>();
CHECK(&p1 == value.get_ptr<test_type*>());
CHECK(p1 == value.get<test_type>());
const test_type& p2 = value.get_ref<const test_type&>();
CHECK(&p2 == value.get_ptr<const test_type*>());
CHECK(p2 == value.get<test_type>());
// check if mismatching references throw correctly
CHECK_THROWS(value.get_ref<json::object_t&>());
CHECK_THROWS(value.get_ref<json::array_t&>());
CHECK_NOTHROW(value.get_ref<json::string_t&>());
CHECK_THROWS(value.get_ref<json::boolean_t&>());
CHECK_THROWS(value.get_ref<json::number_integer_t&>());
CHECK_THROWS(value.get_ref<json::number_float_t&>());
}
SECTION("reference access to boolean_t")
{
using test_type = json::boolean_t;
json value = false;
// check if references are returned correctly
test_type& p1 = value.get_ref<test_type&>();
CHECK(&p1 == value.get_ptr<test_type*>());
CHECK(p1 == value.get<test_type>());
const test_type& p2 = value.get_ref<const test_type&>();
CHECK(&p2 == value.get_ptr<const test_type*>());
CHECK(p2 == value.get<test_type>());
// check if mismatching references throw correctly
CHECK_THROWS(value.get_ref<json::object_t&>());
CHECK_THROWS(value.get_ref<json::array_t&>());
CHECK_THROWS(value.get_ref<json::string_t&>());
CHECK_NOTHROW(value.get_ref<json::boolean_t&>());
CHECK_THROWS(value.get_ref<json::number_integer_t&>());
CHECK_THROWS(value.get_ref<json::number_float_t&>());
}
SECTION("reference access to number_integer_t")
{
using test_type = json::number_integer_t;
json value = 23;
// check if references are returned correctly
test_type& p1 = value.get_ref<test_type&>();
CHECK(&p1 == value.get_ptr<test_type*>());
CHECK(p1 == value.get<test_type>());
const test_type& p2 = value.get_ref<const test_type&>();
CHECK(&p2 == value.get_ptr<const test_type*>());
CHECK(p2 == value.get<test_type>());
// check if mismatching references throw correctly
CHECK_THROWS(value.get_ref<json::object_t&>());
CHECK_THROWS(value.get_ref<json::array_t&>());
CHECK_THROWS(value.get_ref<json::string_t&>());
CHECK_THROWS(value.get_ref<json::boolean_t&>());
CHECK_NOTHROW(value.get_ref<json::number_integer_t&>());
CHECK_THROWS(value.get_ref<json::number_float_t&>());
}
SECTION("reference access to number_float_t")
{
using test_type = json::number_float_t;
json value = 42.23;
// check if references are returned correctly
test_type& p1 = value.get_ref<test_type&>();
CHECK(&p1 == value.get_ptr<test_type*>());
CHECK(p1 == value.get<test_type>());
const test_type& p2 = value.get_ref<const test_type&>();
CHECK(&p2 == value.get_ptr<const test_type*>());
CHECK(p2 == value.get<test_type>());
// check if mismatching references throw correctly
CHECK_THROWS(value.get_ref<json::object_t&>());
CHECK_THROWS(value.get_ref<json::array_t&>());
CHECK_THROWS(value.get_ref<json::string_t&>());
CHECK_THROWS(value.get_ref<json::boolean_t&>());
CHECK_THROWS(value.get_ref<json::number_integer_t&>());
CHECK_NOTHROW(value.get_ref<json::number_float_t&>());
}
}
TEST_CASE("element access")
{
SECTION("array")
......
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