worked on issue #8 and #27

header_only/json.h

@@ -140,7 +140,7 @@ class json
     /// create an object according to given type
     json(const value_t);
     /// create a null object
-    json() = default;
+    json() noexcept;
     /// create a null object
     json(std::nullptr_t) noexcept;
     /// create a string object from a C++ string
@@ -160,7 +160,7 @@ class json
     /// create an object (move)
     json(object_t&&);
     /// create from an initializer list (to an array or object)
-    json(list_init_t);
+    json(list_init_t, bool = true, value_t = value_t::array);
 
     /*!
     @brief create a number object (integer)
@@ -171,7 +171,7 @@ class json
                  std::numeric_limits<T>::is_integer, T>::type
              = 0>
     json(const T n) noexcept
-        : type_(value_t::number),
+        : final_type_(0), type_(value_t::number),
           value_(static_cast<number_t>(n))
     {}
 
@@ -184,7 +184,7 @@ class json
                  std::is_floating_point<T>::value>::type
              >
     json(const T n) noexcept
-        : type_(value_t::number_float),
+        : final_type_(0), type_(value_t::number_float),
           value_(static_cast<number_float_t>(n))
     {}
 
@@ -229,6 +229,11 @@ class json
     /// destructor
     ~json() noexcept;
 
+    /// explicit keyword to force array creation
+    static json array(list_init_t = list_init_t());
+    /// explicit keyword to force object creation
+    static json object(list_init_t = list_init_t());
+
     /// create from string representation
     static json parse(const std::string&);
     /// create from string representation
@@ -404,9 +409,10 @@ class json
     const_reverse_iterator crend() const noexcept;
 
   private:
+    /// whether the type is final
+    unsigned final_type_ : 1;
     /// the type of this object
     value_t type_ = value_t::null;
-
     /// the payload
     value value_ {};
 
@@ -654,6 +660,9 @@ json::json(const value_t t)
     }
 }
 
+json::json() noexcept : final_type_(0), type_(value_t::null)
+{}
+
 /*!
 Construct a null JSON object.
 */
@@ -666,35 +675,35 @@ Construct a string JSON object.
 @param s  a string to initialize the JSON object with
 */
 json::json(const std::string& s)
-    : type_(value_t::string), value_(new string_t(s))
+    : final_type_(0), type_(value_t::string), value_(new string_t(s))
 {}
 
 json::json(std::string&& s)
-    : type_(value_t::string), value_(new string_t(std::move(s)))
+    : final_type_(0), type_(value_t::string), value_(new string_t(std::move(s)))
 {}
 
 json::json(const char* s)
-    : type_(value_t::string), value_(new string_t(s))
+    : final_type_(0), type_(value_t::string), value_(new string_t(s))
 {}
 
 json::json(const bool b) noexcept
-    : type_(value_t::boolean), value_(b)
+    : final_type_(0), type_(value_t::boolean), value_(b)
 {}
 
 json::json(const array_t& a)
-    : type_(value_t::array), value_(new array_t(a))
+    : final_type_(0), type_(value_t::array), value_(new array_t(a))
 {}
 
 json::json(array_t&& a)
-    : type_(value_t::array), value_(new array_t(std::move(a)))
+    : final_type_(0), type_(value_t::array), value_(new array_t(std::move(a)))
 {}
 
 json::json(const object_t& o)
-    : type_(value_t::object), value_(new object_t(o))
+    : final_type_(0), type_(value_t::object), value_(new object_t(o))
 {}
 
 json::json(object_t&& o)
-    : type_(value_t::object), value_(new object_t(std::move(o)))
+    : final_type_(0), type_(value_t::object), value_(new object_t(std::move(o)))
 {}
 
 /*!
@@ -711,33 +720,90 @@ as is to create an array.
 
 @bug With the described approach, we would fail to recognize an array whose
      first element is again an arrays as array.
+
+@param a               an initializer list to create from
+@param type_deduction  whether the type (array/object) shall eb deducted
+@param manual_type     if type deduction is switched of, pass a manual type
 */
-json::json(list_init_t a)
+json::json(list_init_t a, bool type_deduction, value_t manual_type) : final_type_(0)
 {
+    // the initializer list could describe an object
+    bool is_object = true;
+
     // check if each element is an array with two elements whose first element
     // is a string
     for (const auto& element : a)
     {
-        if (element.type_ != value_t::array or
+        if ((element.final_type_ == 1 and element.type_ == value_t::array)
-                element.size() != 2 or
+                or (element.type_ != value_t::array or element.size() != 2 or element[0].type_ != value_t::string))
-                element[0].type_ != value_t::string)
         {
-
+            // we found an element that makes it impossible to use the
-            // the initializer list describes an array
+            // initializer list as object
-            type_ = value_t::array;
+            is_object = false;
-            value_ = new array_t(a);
+            break;
-            return;
         }
     }
 
-    // the initializer list is a list of pairs
+    // adjust type if type deduction is not wanted
-    type_ = value_t::object;
+    if (not type_deduction)
-    value_ = new object_t();
-    for (const json& element : a)
     {
-        const std::string k = element[0];
+        // mark this object's type as final
-        value_.object->emplace(std::make_pair(std::move(k),
+        final_type_ = 1;
-                                              std::move(element[1])));
+
+        // if array is wanted, do not create an object though possible
+        if (manual_type == value_t::array)
+        {
+            is_object = false;
+        }
+
+        // if object is wanted but impossible, throw an exception
+        if (manual_type == value_t::object and not is_object)
+        {
+            throw std::logic_error("cannot create JSON object");
+        }
+    }
+
+    if (is_object)
+    {
+        // the initializer list is a list of pairs -> create object
+        type_ = value_t::object;
+        value_ = new object_t();
+        for (auto& element : a)
+        {
+            value_.object->emplace(std::make_pair(std::move(element[0]), std::move(element[1])));
+        }
+    }
+    else
+    {
+        // the initializer list describes an array -> create array
+        type_ = value_t::array;
+        value_ = new array_t(std::move(a));
+    }
+}
+
+/*!
+@param a  initializer list to create an array from
+@return array
+*/
+json json::array(list_init_t a)
+{
+    return json(a, false, value_t::array);
+}
+
+/*!
+@param a  initializer list to create an object from
+@return object
+*/
+json json::object(list_init_t a)
+{
+    // if more than one element is in the initializer list, wrap it
+    if (a.size() > 1)
+    {
+        return json({a}, false, value_t::object);
+    }
+    else
+    {
+        return json(a, false, value_t::object);
     }
 }
 

src/json.cc

@@ -84,6 +84,9 @@ json::json(const value_t t)
     }
 }
 
+json::json() noexcept : final_type_(0), type_(value_t::null)
+{}
+
 /*!
 Construct a null JSON object.
 */
@@ -96,35 +99,35 @@ Construct a string JSON object.
 @param s  a string to initialize the JSON object with
 */
 json::json(const std::string& s)
-    : type_(value_t::string), value_(new string_t(s))
+    : final_type_(0), type_(value_t::string), value_(new string_t(s))
 {}
 
 json::json(std::string&& s)
-    : type_(value_t::string), value_(new string_t(std::move(s)))
+    : final_type_(0), type_(value_t::string), value_(new string_t(std::move(s)))
 {}
 
 json::json(const char* s)
-    : type_(value_t::string), value_(new string_t(s))
+    : final_type_(0), type_(value_t::string), value_(new string_t(s))
 {}
 
 json::json(const bool b) noexcept
-    : type_(value_t::boolean), value_(b)
+    : final_type_(0), type_(value_t::boolean), value_(b)
 {}
 
 json::json(const array_t& a)
-    : type_(value_t::array), value_(new array_t(a))
+    : final_type_(0), type_(value_t::array), value_(new array_t(a))
 {}
 
 json::json(array_t&& a)
-    : type_(value_t::array), value_(new array_t(std::move(a)))
+    : final_type_(0), type_(value_t::array), value_(new array_t(std::move(a)))
 {}
 
 json::json(const object_t& o)
-    : type_(value_t::object), value_(new object_t(o))
+    : final_type_(0), type_(value_t::object), value_(new object_t(o))
 {}
 
 json::json(object_t&& o)
-    : type_(value_t::object), value_(new object_t(std::move(o)))
+    : final_type_(0), type_(value_t::object), value_(new object_t(std::move(o)))
 {}
 
 /*!
@@ -141,33 +144,90 @@ as is to create an array.
 
 @bug With the described approach, we would fail to recognize an array whose
      first element is again an arrays as array.
+
+@param a               an initializer list to create from
+@param type_deduction  whether the type (array/object) shall eb deducted
+@param manual_type     if type deduction is switched of, pass a manual type
 */
-json::json(list_init_t a)
+json::json(list_init_t a, bool type_deduction, value_t manual_type) : final_type_(0)
 {
+    // the initializer list could describe an object
+    bool is_object = true;
+
     // check if each element is an array with two elements whose first element
     // is a string
     for (const auto& element : a)
     {
-        if (element.type_ != value_t::array or
+        if ((element.final_type_ == 1 and element.type_ == value_t::array)
-                element.size() != 2 or
+                or (element.type_ != value_t::array or element.size() != 2 or element[0].type_ != value_t::string))
-                element[0].type_ != value_t::string)
         {
-
+            // we found an element that makes it impossible to use the
-            // the initializer list describes an array
+            // initializer list as object
-            type_ = value_t::array;
+            is_object = false;
-            value_ = new array_t(a);
+            break;
-            return;
         }
     }
 
-    // the initializer list is a list of pairs
+    // adjust type if type deduction is not wanted
-    type_ = value_t::object;
+    if (not type_deduction)
-    value_ = new object_t();
-    for (const json& element : a)
     {
-        const std::string k = element[0];
+        // mark this object's type as final
-        value_.object->emplace(std::make_pair(std::move(k),
+        final_type_ = 1;
-                                              std::move(element[1])));
+
+        // if array is wanted, do not create an object though possible
+        if (manual_type == value_t::array)
+        {
+            is_object = false;
+        }
+
+        // if object is wanted but impossible, throw an exception
+        if (manual_type == value_t::object and not is_object)
+        {
+            throw std::logic_error("cannot create JSON object");
+        }
+    }
+
+    if (is_object)
+    {
+        // the initializer list is a list of pairs -> create object
+        type_ = value_t::object;
+        value_ = new object_t();
+        for (auto& element : a)
+        {
+            value_.object->emplace(std::make_pair(std::move(element[0]), std::move(element[1])));
+        }
+    }
+    else
+    {
+        // the initializer list describes an array -> create array
+        type_ = value_t::array;
+        value_ = new array_t(std::move(a));
+    }
+}
+
+/*!
+@param a  initializer list to create an array from
+@return array
+*/
+json json::array(list_init_t a)
+{
+    return json(a, false, value_t::array);
+}
+
+/*!
+@param a  initializer list to create an object from
+@return object
+*/
+json json::object(list_init_t a)
+{
+    // if more than one element is in the initializer list, wrap it
+    if (a.size() > 1)
+    {
+        return json({a}, false, value_t::object);
+    }
+    else
+    {
+        return json(a, false, value_t::object);
     }
 }
 

src/json.h

@@ -140,7 +140,7 @@ class json
     /// create an object according to given type
     json(const value_t);
     /// create a null object
-    json() = default;
+    json() noexcept;
     /// create a null object
     json(std::nullptr_t) noexcept;
     /// create a string object from a C++ string
@@ -160,7 +160,7 @@ class json
     /// create an object (move)
     json(object_t&&);
     /// create from an initializer list (to an array or object)
-    json(list_init_t);
+    json(list_init_t, bool = true, value_t = value_t::array);
 
     /*!
     @brief create a number object (integer)
@@ -171,7 +171,7 @@ class json
                  std::numeric_limits<T>::is_integer, T>::type
              = 0>
     json(const T n) noexcept
-        : type_(value_t::number),
+        : final_type_(0), type_(value_t::number),
           value_(static_cast<number_t>(n))
     {}
 
@@ -184,7 +184,7 @@ class json
                  std::is_floating_point<T>::value>::type
              >
     json(const T n) noexcept
-        : type_(value_t::number_float),
+        : final_type_(0), type_(value_t::number_float),
           value_(static_cast<number_float_t>(n))
     {}
 
@@ -229,6 +229,11 @@ class json
     /// destructor
     ~json() noexcept;
 
+    /// explicit keyword to force array creation
+    static json array(list_init_t = list_init_t());
+    /// explicit keyword to force object creation
+    static json object(list_init_t = list_init_t());
+
     /// create from string representation
     static json parse(const std::string&);
     /// create from string representation
@@ -404,9 +409,10 @@ class json
     const_reverse_iterator crend() const noexcept;
 
   private:
+    /// whether the type is final
+    unsigned final_type_ : 1;
     /// the type of this object
     value_t type_ = value_t::null;
-
     /// the payload
     value value_ {};
 

test/json_unit.cc

@@ -304,13 +304,70 @@ TEST_CASE("array")
                 CHECK(v == vec[static_cast<size_t>(v)]);
             }
         }
+    }
 
-
+    SECTION("Initializer lists")
+    {
         // edge case: This should be an array with two elements which are in
         // turn arrays with two strings. However, this is treated like the
         // initializer list of an object.
         json j_should_be_an_array = { {"foo", "bar"}, {"baz", "bat"} };
         CHECK(j_should_be_an_array.type() == json::value_t::object);
+
+        json j_is_an_array = { json::array({"foo", "bar"}), {"baz", "bat"} };
+        CHECK(j_is_an_array.type() == json::value_t::array);
+
+        // array outside initializer list
+        json j_pair_array = json::array({"s1", "s2"});
+        CHECK(j_pair_array.type() == json::value_t::array);
+
+        // array inside initializer list
+        json j_pair_array2 = {json::array({"us1", "us2"})};
+        CHECK(j_pair_array2.type() == json::value_t::array);
+
+        // array() is []
+        json j_empty_array_explicit = json::array();
+        CHECK(j_empty_array_explicit.type() == json::value_t::array);
+
+        // object() is []
+        json j_empty_object_explicit = json::object();
+        CHECK(j_empty_object_explicit.type() == json::value_t::object);
+
+        // {object({"s1", "s2"})} is [{"s1": "s2"}]
+        json j_explicit_object = {json::object({"s1", "s2"})};
+        CHECK(j_explicit_object.type() == json::value_t::array);
+
+        // object({"s1", "s2"}) is [{"s1": "s2"}]
+        json j_explicit_object2 = json::object({"s1", "s2"});
+        CHECK(j_explicit_object2.type() == json::value_t::object);
+
+        // object({{"s1", "s2"}}) is [{"s1": "s2"}]
+        json j_explicit_object3 = json::object({{"s1", "s2"}});
+        CHECK(j_explicit_object3.type() == json::value_t::object);
+
+        // check errors when explicit object creation is demanded
+        CHECK_THROWS_AS(json::object({"s1"}), std::logic_error);
+        CHECK_THROWS_AS(json::object({"s1", 1, 3}), std::logic_error);
+        CHECK_THROWS_AS(json::object({1, "s1"}), std::logic_error);
+        CHECK_THROWS_AS(json::object({{1, "s1"}}), std::logic_error);
+        CHECK_THROWS_AS(json::object({{"foo", "bar"}, {1, "s1"}}), std::logic_error);
+
+        // {} is null
+        json j_null = {};
+        CHECK(j_null.type() == json::value_t::null);
+
+        // {{}} is []
+        json j_empty_array_implicit = {{}};
+        CHECK(j_empty_array_implicit.type() == json::value_t::array);
+
+        // {1} is [1]
+        json j_singleton_array = {1};
+        CHECK(j_singleton_array.type() == json::value_t::array);
+
+        // test case from issue #8
+        json j_issue8 = {json::array({"a", "b"}), json::array({"c", "d"})};
+        CHECK(j_issue8.type() == json::value_t::array);
+        CHECK(j_issue8.dump() == "[[\"a\",\"b\"],[\"c\",\"d\"]]");
     }
 
     SECTION("Iterators and empty arrays")