Merge pull request #663 from himikof/move-construction

Support moving from rvalues in std::initializer_list

src/json.hpp

@@ -575,6 +575,14 @@ struct external_constructor<value_t::string>
         j.m_value = s;
         j.assert_invariant();
     }
+
+    template<typename BasicJsonType>
+    static void construct(BasicJsonType& j, typename BasicJsonType::string_t&&  s)
+    {
+        j.m_type = value_t::string;
+        j.m_value = std::move(s);
+        j.assert_invariant();
+    }
 };
 
 template<>
@@ -624,6 +632,14 @@ struct external_constructor<value_t::array>
         j.assert_invariant();
     }
 
+    template<typename BasicJsonType>
+    static void construct(BasicJsonType& j, typename BasicJsonType::array_t&&  arr)
+    {
+        j.m_type = value_t::array;
+        j.m_value = std::move(arr);
+        j.assert_invariant();
+    }
+
     template<typename BasicJsonType, typename CompatibleArrayType,
              enable_if_t<not std::is_same<CompatibleArrayType,
                                           typename BasicJsonType::array_t>::value,
@@ -662,6 +678,14 @@ struct external_constructor<value_t::object>
         j.assert_invariant();
     }
 
+    template<typename BasicJsonType>
+    static void construct(BasicJsonType& j, typename BasicJsonType::object_t&&  obj)
+    {
+        j.m_type = value_t::object;
+        j.m_value = std::move(obj);
+        j.assert_invariant();
+    }
+
     template<typename BasicJsonType, typename CompatibleObjectType,
              enable_if_t<not std::is_same<CompatibleObjectType,
                                           typename BasicJsonType::object_t>::value, int> = 0>
@@ -850,6 +874,12 @@ void to_json(BasicJsonType& j, const CompatibleString& s)
     external_constructor<value_t::string>::construct(j, s);
 }
 
+template <typename BasicJsonType>
+void to_json(BasicJsonType& j, typename BasicJsonType::string_t&&  s)
+{
+    external_constructor<value_t::string>::construct(j, std::move(s));
+}
+
 template<typename BasicJsonType, typename FloatType,
          enable_if_t<std::is_floating_point<FloatType>::value, int> = 0>
 void to_json(BasicJsonType& j, FloatType val) noexcept
@@ -900,13 +930,25 @@ void to_json(BasicJsonType& j, const  CompatibleArrayType& arr)
     external_constructor<value_t::array>::construct(j, arr);
 }
 
+template <typename BasicJsonType>
+void to_json(BasicJsonType& j, typename BasicJsonType::array_t&&  arr)
+{
+    external_constructor<value_t::array>::construct(j, std::move(arr));
+}
+
 template <
     typename BasicJsonType, typename CompatibleObjectType,
     enable_if_t<is_compatible_object_type<BasicJsonType, CompatibleObjectType>::value,
                 int> = 0 >
-void to_json(BasicJsonType& j, const  CompatibleObjectType& arr)
+void to_json(BasicJsonType& j, const  CompatibleObjectType& obj)
 {
-    external_constructor<value_t::object>::construct(j, arr);
+    external_constructor<value_t::object>::construct(j, obj);
+}
+
+template <typename BasicJsonType>
+void to_json(BasicJsonType& j, typename BasicJsonType::object_t&&  obj)
+{
+    external_constructor<value_t::object>::construct(j, std::move(obj));
 }
 
 template<typename BasicJsonType, typename T, std::size_t N,
@@ -6799,6 +6841,67 @@ class serializer
     /// the indentation string
     string_t indent_string;
 };
+
+template<typename BasicJsonType>
+struct json_ref
+{
+    typedef BasicJsonType value_type;
+
+    json_ref(value_type&&  value)
+        : owned_value_(std::move(value))
+        , is_rvalue_(true)
+    {
+        value_ref_ = &owned_value_;
+    }
+
+    json_ref(const value_type& value)
+        : value_ref_(const_cast<value_type*>(&value))
+        , is_rvalue_(false)
+    {}
+
+    json_ref(std::initializer_list<json_ref> init)
+        : owned_value_(init)
+        , is_rvalue_(true)
+    {
+        value_ref_ = &owned_value_;
+    }
+
+    template <class... Args>
+    json_ref(Args... args)
+        : owned_value_(std::forward<Args>(args)...)
+        , is_rvalue_(true)
+    {
+        value_ref_ = &owned_value_;
+    }
+
+    value_type moved_or_copied() const
+    {
+        if (is_rvalue_)
+        {
+            return std::move(*value_ref_);
+        }
+        else
+        {
+            return *value_ref_;
+        }
+    }
+
+    value_type const& operator*() const
+    {
+        return *static_cast<value_type const*>(value_ref_);
+    }
+
+    value_type const* operator->() const
+    {
+        return static_cast<value_type const*>(value_ref_);
+    }
+
+  private:
+    value_type * value_ref_;
+    mutable value_type owned_value_;
+    bool is_rvalue_;
+};
+
 } // namespace detail
 
 /// namespace to hold default `to_json` / `from_json` functions
@@ -7297,6 +7400,7 @@ class basic_json
     template<typename T, typename SFINAE>
     using json_serializer = JSONSerializer<T, SFINAE>;
 
+    using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
     ////////////////
     // exceptions //
@@ -8025,18 +8129,36 @@ class basic_json
             string = create<string_t>(value);
         }
 
+        /// constructor for rvalue strings
+        json_value(string_t&&  value)
+        {
+            string = create<string_t>(std::move(value));
+        }
+
         /// constructor for objects
         json_value(const object_t& value)
         {
             object = create<object_t>(value);
         }
 
+        /// constructor for rvalue objects
+        json_value(object_t&&  value)
+        {
+            object = create<object_t>(std::move(value));
+        }
+
         /// constructor for arrays
         json_value(const array_t& value)
         {
             array = create<array_t>(value);
         }
 
+        /// constructor for rvalue arrays
+        json_value(array_t&&  value)
+        {
+            array = create<array_t>(std::move(value));
+        }
+
         void destroy(value_t t)
         {
             switch (t)
@@ -8310,10 +8432,10 @@ class basic_json
     With the rules described above, the following JSON values cannot be
     expressed by an initializer list:
 
-    - the empty array (`[]`): use @ref array(std::initializer_list<basic_json>)
+    - the empty array (`[]`): use @ref array(initializer_list_t)
       with an empty initializer list in this case
     - arrays whose elements satisfy rule 2: use @ref
-      array(std::initializer_list<basic_json>) with the same initializer list
+      array(initializer_list_t) with the same initializer list
       in this case
 
     @note When used without parentheses around an empty initializer list, @ref
@@ -8325,8 +8447,8 @@ class basic_json
     @param[in] type_deduction internal parameter; when set to `true`, the type
     of the JSON value is deducted from the initializer list @a init; when set
     to `false`, the type provided via @a manual_type is forced. This mode is
-    used by the functions @ref array(std::initializer_list<basic_json>) and
+    used by the functions @ref array(initializer_list_t) and
-    @ref object(std::initializer_list<basic_json>).
+    @ref object(initializer_list_t).
 
     @param[in] manual_type internal parameter; when @a type_deduction is set
     to `false`, the created JSON value will use the provided type (only @ref
@@ -8337,7 +8459,7 @@ class basic_json
     `value_t::object`, but @a init contains an element which is not a pair
     whose first element is a string. In this case, the constructor could not
     create an object. If @a type_deduction would have be `true`, an array
-    would have been created. See @ref object(std::initializer_list<basic_json>)
+    would have been created. See @ref object(initializer_list_t)
     for an example.
 
     @complexity Linear in the size of the initializer list @a init.
@@ -8345,23 +8467,23 @@ class basic_json
     @liveexample{The example below shows how JSON values are created from
     initializer lists.,basic_json__list_init_t}
 
-    @sa @ref array(std::initializer_list<basic_json>) -- create a JSON array
+    @sa @ref array(initializer_list_t) -- create a JSON array
     value from an initializer list
-    @sa @ref object(std::initializer_list<basic_json>) -- create a JSON object
+    @sa @ref object(initializer_list_t) -- create a JSON object
     value from an initializer list
 
     @since version 1.0.0
     */
-    basic_json(std::initializer_list<basic_json> init,
+    basic_json(initializer_list_t init,
                bool type_deduction = true,
                value_t manual_type = value_t::array)
     {
         // check if each element is an array with two elements whose first
         // element is a string
         bool is_an_object = std::all_of(init.begin(), init.end(),
-                                        [](const basic_json & element)
+                                        [](const detail::json_ref<basic_json>& element_ref)
         {
-            return (element.is_array() and element.size() == 2 and element[0].is_string());
+            return (element_ref->is_array() and element_ref->size() == 2 and (*element_ref)[0].is_string());
         });
 
         // adjust type if type deduction is not wanted
@@ -8386,16 +8508,19 @@ class basic_json
             m_type = value_t::object;
             m_value = value_t::object;
 
-            std::for_each(init.begin(), init.end(), [this](const basic_json & element)
+            std::for_each(init.begin(), init.end(), [this](const detail::json_ref<basic_json>& element_ref)
             {
-                m_value.object->emplace(*(element[0].m_value.string), element[1]);
+                basic_json element = element_ref.moved_or_copied();
+                m_value.object->emplace(
+                    std::move(*((*element.m_value.array)[0].m_value.string)),
+                    std::move((*element.m_value.array)[1]));
             });
         }
         else
         {
             // the initializer list describes an array -> create array
             m_type = value_t::array;
-            m_value.array = create<array_t>(init);
+            m_value.array = create<array_t>(init.begin(), init.end());
         }
 
         assert_invariant();
@@ -8410,7 +8535,7 @@ class basic_json
 
     @note This function is only needed to express two edge cases that cannot
     be realized with the initializer list constructor (@ref
-    basic_json(std::initializer_list<basic_json>, bool, value_t)). These cases
+    basic_json(initializer_list_t, bool, value_t)). These cases
     are:
     1. creating an array whose elements are all pairs whose first element is a
     string -- in this case, the initializer list constructor would create an
@@ -8428,15 +8553,14 @@ class basic_json
     @liveexample{The following code shows an example for the `array`
     function.,array}
 
-    @sa @ref basic_json(std::initializer_list<basic_json>, bool, value_t) --
+    @sa @ref basic_json(initializer_list_t, bool, value_t) --
     create a JSON value from an initializer list
-    @sa @ref object(std::initializer_list<basic_json>) -- create a JSON object
+    @sa @ref object(initializer_list_t) -- create a JSON object
     value from an initializer list
 
     @since version 1.0.0
     */
-    static basic_json array(std::initializer_list<basic_json> init =
+    static basic_json array(initializer_list_t init = {})
-                                std::initializer_list<basic_json>())
     {
         return basic_json(init, false, value_t::array);
     }
@@ -8449,10 +8573,10 @@ class basic_json
     the initializer list is empty, the empty object `{}` is created.
 
     @note This function is only added for symmetry reasons. In contrast to the
-    related function @ref array(std::initializer_list<basic_json>), there are
+    related function @ref array(initializer_list_t), there are
     no cases which can only be expressed by this function. That is, any
     initializer list @a init can also be passed to the initializer list
-    constructor @ref basic_json(std::initializer_list<basic_json>, bool, value_t).
+    constructor @ref basic_json(initializer_list_t, bool, value_t).
 
     @param[in] init  initializer list to create an object from (optional)
 
@@ -8460,7 +8584,7 @@ class basic_json
 
     @throw type_error.301 if @a init is not a list of pairs whose first
     elements are strings. In this case, no object can be created. When such a
-    value is passed to @ref basic_json(std::initializer_list<basic_json>, bool, value_t),
+    value is passed to @ref basic_json(initializer_list_t, bool, value_t),
     an array would have been created from the passed initializer list @a init.
     See example below.
 
@@ -8469,15 +8593,14 @@ class basic_json
     @liveexample{The following code shows an example for the `object`
     function.,object}
 
-    @sa @ref basic_json(std::initializer_list<basic_json>, bool, value_t) --
+    @sa @ref basic_json(initializer_list_t, bool, value_t) --
     create a JSON value from an initializer list
-    @sa @ref array(std::initializer_list<basic_json>) -- create a JSON array
+    @sa @ref array(initializer_list_t) -- create a JSON array
     value from an initializer list
 
     @since version 1.0.0
     */
-    static basic_json object(std::initializer_list<basic_json> init =
+    static basic_json object(initializer_list_t init = {})
-                                 std::initializer_list<basic_json>())
     {
         return basic_json(init, false, value_t::object);
     }
@@ -8650,6 +8773,11 @@ class basic_json
     // other constructors and destructor //
     ///////////////////////////////////////
 
+    basic_json(const detail::json_ref<basic_json>& ref)
+        : basic_json(ref.moved_or_copied())
+    {
+    }
+
     /*!
     @brief copy constructor
 
@@ -11565,12 +11693,13 @@ class basic_json
     @liveexample{The example shows how initializer lists are treated as
     objects when possible.,push_back__initializer_list}
     */
-    void push_back(std::initializer_list<basic_json> init)
+    void push_back(initializer_list_t init)
     {
-        if (is_object() and init.size() == 2 and init.begin()->is_string())
+        if (is_object() and init.size() == 2 and (*init.begin())->is_string())
         {
-            const string_t key = *init.begin();
+            basic_json&&  key = init.begin()->moved_or_copied();
-            push_back(typename object_t::value_type(key, *(init.begin() + 1)));
+            push_back(typename object_t::value_type(
+                        std::move(key.get_ref<string_t&>()), (init.begin() + 1)->moved_or_copied()));
         }
         else
         {
@@ -11580,9 +11709,9 @@ class basic_json
 
     /*!
     @brief add an object to an object
-    @copydoc push_back(std::initializer_list<basic_json>)
+    @copydoc push_back(initializer_list_t)
     */
-    reference operator+=(std::initializer_list<basic_json> init)
+    reference operator+=(initializer_list_t init)
     {
         push_back(init);
         return *this;
@@ -11867,7 +11996,7 @@ class basic_json
 
     @since version 1.0.0
     */
-    iterator insert(const_iterator pos, std::initializer_list<basic_json> ilist)
+    iterator insert(const_iterator pos, initializer_list_t ilist)
     {
         // insert only works for arrays
         if (JSON_UNLIKELY(not is_array()))
@@ -11883,7 +12012,7 @@ class basic_json
 
         // insert to array and return iterator
         iterator result(this);
-        result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, ilist);
+        result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, ilist.begin(), ilist.end());
         return result;
     }
 

test/src/unit-constructor1.cpp

@@ -842,8 +842,7 @@ TEST_CASE("constructors")
         {
             SECTION("explicit")
             {
-                std::initializer_list<json> l;
+                json j(json::initializer_list_t {});
-                json j(l);
                 CHECK(j.type() == json::value_t::object);
             }
 
@@ -860,8 +859,7 @@ TEST_CASE("constructors")
             {
                 SECTION("explicit")
                 {
-                    std::initializer_list<json> l = {json(json::array_t())};
+                    json j(json::initializer_list_t {json(json::array_t())});
-                    json j(l);
                     CHECK(j.type() == json::value_t::array);
                 }
 
@@ -876,8 +874,7 @@ TEST_CASE("constructors")
             {
                 SECTION("explicit")
                 {
-                    std::initializer_list<json> l = {json(json::object_t())};
+                    json j(json::initializer_list_t {json(json::object_t())});
-                    json j(l);
                     CHECK(j.type() == json::value_t::array);
                 }
 
@@ -892,8 +889,7 @@ TEST_CASE("constructors")
             {
                 SECTION("explicit")
                 {
-                    std::initializer_list<json> l = {json("Hello world")};
+                    json j(json::initializer_list_t {json("Hello world")});
-                    json j(l);
                     CHECK(j.type() == json::value_t::array);
                 }
 
@@ -908,8 +904,7 @@ TEST_CASE("constructors")
             {
                 SECTION("explicit")
                 {
-                    std::initializer_list<json> l = {json(true)};
+                    json j(json::initializer_list_t {json(true)});
-                    json j(l);
                     CHECK(j.type() == json::value_t::array);
                 }
 
@@ -924,8 +919,7 @@ TEST_CASE("constructors")
             {
                 SECTION("explicit")
                 {
-                    std::initializer_list<json> l = {json(1)};
+                    json j(json::initializer_list_t {json(1)});
-                    json j(l);
                     CHECK(j.type() == json::value_t::array);
                 }
 
@@ -940,8 +934,7 @@ TEST_CASE("constructors")
             {
                 SECTION("explicit")
                 {
-                    std::initializer_list<json> l = {json(1u)};
+                    json j(json::initializer_list_t {json(1u)});
-                    json j(l);
                     CHECK(j.type() == json::value_t::array);
                 }
 
@@ -956,8 +949,7 @@ TEST_CASE("constructors")
             {
                 SECTION("explicit")
                 {
-                    std::initializer_list<json> l = {json(42.23)};
+                    json j(json::initializer_list_t {json(42.23)});
-                    json j(l);
                     CHECK(j.type() == json::value_t::array);
                 }
 
@@ -973,8 +965,7 @@ TEST_CASE("constructors")
         {
             SECTION("explicit")
             {
-                std::initializer_list<json> l = {1, 1u, 42.23, true, nullptr, json::object_t(), json::array_t()};
+                json j(json::initializer_list_t {1, 1u, 42.23, true, nullptr, json::object_t(), json::array_t()});
-                json j(l);
                 CHECK(j.type() == json::value_t::array);
             }
 
@@ -1034,6 +1025,125 @@ TEST_CASE("constructors")
                 CHECK(j.type() == json::value_t::array);
             }
         }
+
+        SECTION("move from initializer_list")
+        {
+            SECTION("string")
+            {
+                // This should break through any short string optimization in std::string
+                std::string source(1024, '!');
+                const char* source_addr = source.data();
+
+                SECTION("constructor with implicit types (array)")
+                {
+                    json j = {std::move(source)};
+                    CHECK(j[0].get_ref<std::string const&>().data() == source_addr);
+                }
+
+                SECTION("constructor with implicit types (object)")
+                {
+                    json j = {{"key", std::move(source)}};
+                    CHECK(j["key"].get_ref<std::string const&>().data() == source_addr);
+                }
+
+                SECTION("constructor with implicit types (object key)")
+                {
+                    json j = {{std::move(source), 42}};
+                    CHECK(j.get_ref<json::object_t&>().begin()->first.data() == source_addr);
+                }
+            }
+
+            SECTION("array")
+            {
+                json::array_t source = {1, 2, 3};
+                const json* source_addr = source.data();
+
+                SECTION("constructor with implicit types (array)")
+                {
+                    json j {std::move(source)};
+                    CHECK(j[0].get_ref<json::array_t const&>().data() == source_addr);
+                }
+
+                SECTION("constructor with implicit types (object)")
+                {
+                    json j {{"key", std::move(source)}};
+                    CHECK(j["key"].get_ref<json::array_t const&>().data() == source_addr);
+                }
+
+                SECTION("assignment with implicit types (array)")
+                {
+                    json j = {std::move(source)};
+                    CHECK(j[0].get_ref<json::array_t const&>().data() == source_addr);
+                }
+
+                SECTION("assignment with implicit types (object)")
+                {
+                    json j = {{"key", std::move(source)}};
+                    CHECK(j["key"].get_ref<json::array_t const&>().data() == source_addr);
+                }
+            }
+
+            SECTION("object")
+            {
+                json::object_t source = {{"hello", "world"}};
+                const json* source_addr = &source.at("hello");
+
+                SECTION("constructor with implicit types (array)")
+                {
+                    json j {std::move(source)};
+                    CHECK(&(j[0].get_ref<json::object_t const&>().at("hello")) == source_addr);
+                }
+
+                SECTION("constructor with implicit types (object)")
+                {
+                    json j {{"key", std::move(source)}};
+                    CHECK(&(j["key"].get_ref<json::object_t const&>().at("hello")) == source_addr);
+                }
+
+                SECTION("assignment with implicit types (array)")
+                {
+                    json j = {std::move(source)};
+                    CHECK(&(j[0].get_ref<json::object_t const&>().at("hello")) == source_addr);
+                }
+
+                SECTION("assignment with implicit types (object)")
+                {
+                    json j = {{"key", std::move(source)}};
+                    CHECK(&(j["key"].get_ref<json::object_t const&>().at("hello")) == source_addr);
+                }
+            }
+
+            SECTION("json")
+            {
+                json source {1, 2, 3};
+                const json* source_addr = &source[0];
+
+                SECTION("constructor with implicit types (array)")
+                {
+                    json j {std::move(source), {}};
+                    CHECK(&j[0][0] == source_addr);
+                }
+
+                SECTION("constructor with implicit types (object)")
+                {
+                    json j {{"key", std::move(source)}};
+                    CHECK(&j["key"][0] == source_addr);
+                }
+
+                SECTION("assignment with implicit types (array)")
+                {
+                    json j = {std::move(source), {}};
+                    CHECK(&j[0][0] == source_addr);
+                }
+
+                SECTION("assignment with implicit types (object)")
+                {
+                    json j = {{"key", std::move(source)}};
+                    CHECK(&j["key"][0] == source_addr);
+                }
+            }
+
+        }
     }
 
     SECTION("create an array of n copies of a given value")