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worked on #91
- implemented `get_ptr` function to return pointer to value member - overworked `get` function to support pointer types - added test cases - added documentation (see http://nlohmann.github.io/json/classnlohmann_1_1basic__json.html) with examples
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Niels
@ -1787,24 +1787,192 @@ class basic_json
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}
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}
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/// get a pointer to the value (object)
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const object_t* get_impl_ptr(object_t*) const noexcept
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{
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return is_object() ? m_value.object : nullptr;
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}
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/// get a pointer to the value (array)
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const array_t* get_impl_ptr(array_t*) const noexcept
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{
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return is_array() ? m_value.array : nullptr;
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}
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/// get a pointer to the value (string)
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const string_t* get_impl_ptr(string_t*) const noexcept
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{
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return is_string() ? m_value.string : nullptr;
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}
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/// get a pointer to the value (boolean)
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const boolean_t* get_impl_ptr(boolean_t*) const noexcept
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{
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return is_boolean() ? &m_value.boolean : nullptr;
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}
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/// get a pointer to the value (integer number)
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const number_integer_t* get_impl_ptr(number_integer_t*) const noexcept
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{
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return is_number_integer() ? &m_value.number_integer : nullptr;
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}
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/// get a pointer to the value (floating-point number)
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const number_float_t* get_impl_ptr(number_float_t*) const noexcept
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{
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return is_number_float() ? &m_value.number_float : nullptr;
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}
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public:
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/// @name value access
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/// @{
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/// get a value (explicit)
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// <http://stackoverflow.com/a/8315197/266378>
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template<typename T>
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T get() const
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/*!
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@brief get a value (explicit)
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Explicit type conversion between the JSON value and a compatible value.
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@tparam ValueType non-pointer type compatible to the JSON value, for
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instance `int` for JSON integer numbers, `bool` for JSON booleans, or
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`std::vector` types for JSON arrays
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@return copy of the JSON value, converted to type @a ValueType
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@throw std::domain_error in case passed type @a ValueType is incompatible
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to JSON
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@complexity Linear in the size of the JSON value.
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@liveexample{The example below shows serveral conversions from JSON values
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to other types. There a few things to note: (1) Floating-point numbers can
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be converted to integers\, (2) A JSON array can be converted to a standard
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`std::vector<short>`\, (3) A JSON object can be converted to C++
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assiciative containers such as `std::unordered_map<std::string\,
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json>`.,get__ValueType_const}
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@internal
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The idea of using a casted null pointer to choose the correct
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implementation is from <http://stackoverflow.com/a/8315197/266378>.
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@endinternal
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@sa @ref operator ValueType() const for implicit conversion
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@sa @ref get() for pointer-member access
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*/
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template<typename ValueType, typename
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std::enable_if<
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not std::is_pointer<ValueType>::value
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, int>::type = 0>
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ValueType get() const
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{
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return get_impl(static_cast<T*>(nullptr));
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return get_impl(static_cast<ValueType*>(nullptr));
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}
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/// get a value (implicit)
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template<typename T>
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operator T() const
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/*!
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@brief get a pointer value (explicit)
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Explicit pointer access to the internally stored JSON value. No copies are
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made.
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@warning Writing data to the pointee of the result yields an undefined
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state.
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@tparam PointerType pointer type; must be a pointer to @ref array_t, @ref
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object_t, @ref string_t, @ref boolean_t, @ref number_integer_t, or @ref
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number_float_t.
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@return pointer to the internally stored JSON value if the requested pointer
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type @a PointerType fits to the JSON value; `nullptr` otherwise
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@complexity Constant.
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@liveexample{The example below shows how pointers to internal values of a
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JSON value can be requested. Note that no type conversions are made and a
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`nullptr` is returned if the value and the requested pointer type does not
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match.,get__PointerType}
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@sa @ref get_ptr() for explicit pointer-member access
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*/
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template<typename PointerType, typename
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std::enable_if<
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std::is_pointer<PointerType>::value
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, int>::type = 0>
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PointerType get() const noexcept
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{
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return get<T>();
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// delegate the call to get_ptr
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return get_ptr<PointerType>();
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}
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/*!
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@brief get a pointer value (implicit)
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Implict pointer access to the internally stored JSON value. No copies are
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made.
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@warning Writing data to the pointee of the result yields an undefined
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state.
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@tparam PointerType pointer type; must be a pointer to @ref array_t, @ref
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object_t, @ref string_t, @ref boolean_t, @ref number_integer_t, or @ref
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number_float_t.
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@return pointer to the internally stored JSON value if the requested pointer
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type @a PointerType fits to the JSON value; `nullptr` otherwise
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@complexity Constant.
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@liveexample{The example below shows how pointers to internal values of a
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JSON value can be requested. Note that no type conversions are made and a
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`nullptr` is returned if the value and the requested pointer type does not
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match.,get_ptr}
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*/
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template<typename PointerType, typename
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std::enable_if<
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std::is_pointer<PointerType>::value
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, int>::type = 0>
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PointerType get_ptr() const noexcept
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{
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// get_impl_ptr will only work with non-const and non-volatile pointer
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// types. Therefore, we case away all cv properties to be able to
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// select the correct function. The cv properties will then be added
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// again by the const const cast to PointerType.
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return const_cast<PointerType>(get_impl_ptr(
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static_cast<typename std::add_pointer<typename std::remove_cv<typename std::remove_pointer<PointerType>::type>::type>::type>
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(nullptr)));
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}
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/*!
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@brief get a value (implicit)
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Implict type conversion between the JSON value and a compatible value. The
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call is realized by calling @ref get() const.
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@tparam ValueType non-pointer type compatible to the JSON value, for
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instance `int` for JSON integer numbers, `bool` for JSON booleans, or
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`std::vector` types for JSON arrays
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@return copy of the JSON value, converted to type @a ValueType
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@throw std::domain_error in case passed type @a ValueType is incompatible
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to JSON, thrown by @ref get() const
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@complexity Linear in the size of the JSON value.
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@liveexample{The example below shows serveral conversions from JSON values
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to other types. There a few things to note: (1) Floating-point numbers can
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be converted to integers\, (2) A JSON array can be converted to a standard
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`std::vector<short>`\, (3) A JSON object can be converted to C++
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assiciative containers such as `std::unordered_map<std::string\,
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json>`.,operator__ValueType}
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*/
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template<typename ValueType, typename
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std::enable_if<
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not std::is_pointer<ValueType>::value
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, int>::type = 0>
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operator ValueType() const
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{
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// delegate the call to get<>() const
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return get<ValueType>();
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}
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/// @}
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