iterator_wrapper for const objects (#83)

README.md

@@ -398,7 +398,7 @@ $ make
 $ ./json_unit "*"
 
 ===============================================================================
-All tests passed (3341888 assertions in 28 test cases)
+All tests passed (3341947 assertions in 28 test cases)
 ```
 
 For more information, have a look at the file [.travis.yml](https://github.com/nlohmann/json/blob/master/.travis.yml).

src/json.hpp

@@ -6152,43 +6152,35 @@ class basic_json
         }
     };
 
-    /*!
-    @brief wrapper to access iterator member functions in range-based for
 
-    This class allows to access @ref iterator::key() and @ref iterator::value()
+  private:
-    during range-based for loops. In these loops, a reference to the JSON
+    /// proxy class for the iterator_wrapper functions
-    values is returned, so there is no access to the underlying iterator.
+    template<typename IteratorType>
-    */
+    class iteration_proxy
-    class iterator_wrapper
     {
       private:
-        /// the container to iterate
+        /// helper class for iteration
-        typename basic_json::reference container;
+        class iteration_proxy_internal
-        /// the type of the iterator to use while iteration
-        using json_iterator = decltype(std::begin(container));
-
-        /// internal iterator wrapper
-        class iterator_wrapper_internal
         {
           private:
             /// the iterator
-            json_iterator anchor;
+            IteratorType anchor;
             /// an index for arrays
             size_t array_index = 0;
 
           public:
-            /// construct wrapper given an iterator
+            iteration_proxy_internal(IteratorType it)
-            iterator_wrapper_internal(json_iterator i) : anchor(i)
+                : anchor(it)
             {}
 
             /// dereference operator (needed for range-based for)
-            iterator_wrapper_internal& operator*()
+            iteration_proxy_internal& operator*()
             {
                 return *this;
             }
 
             /// increment operator (needed for range-based for)
-            iterator_wrapper_internal& operator++()
+            iteration_proxy_internal& operator++()
             {
                 ++anchor;
                 ++array_index;
@@ -6197,7 +6189,7 @@ class basic_json
             }
 
             /// inequality operator (needed for range-based for)
-            bool operator!= (const iterator_wrapper_internal& o)
+            bool operator!= (const iteration_proxy_internal& o)
             {
                 return anchor != o.anchor;
             }
@@ -6228,31 +6220,57 @@ class basic_json
             }
 
             /// return value of the iterator
-            typename json_iterator::reference value() const
+            typename IteratorType::reference value() const
             {
                 return anchor.value();
             }
         };
 
+        /// the container to iterate
+        typename IteratorType::reference container;
+
       public:
-        /// construct iterator wrapper from a container
+        /// construct iteration proxy from a container
-        iterator_wrapper(typename basic_json::reference cont)
+        iteration_proxy(typename IteratorType::reference cont)
             : container(cont)
         {}
 
         /// return iterator begin (needed for range-based for)
-        iterator_wrapper_internal begin()
+        iteration_proxy_internal begin()
         {
-            return iterator_wrapper_internal(container.begin());
+            return iteration_proxy_internal(container.begin());
         }
 
         /// return iterator end (needed for range-based for)
-        iterator_wrapper_internal end()
+        iteration_proxy_internal end()
         {
-            return iterator_wrapper_internal(container.end());
+            return iteration_proxy_internal(container.end());
         }
     };
 
+  public:
+    /*!
+    @brief wrapper to access iterator member functions in range-based for
+
+    This functuion allows to access @ref iterator::key() and @ref
+    iterator::value() during range-based for loops. In these loops, a reference
+    to the JSON values is returned, so there is no access to the underlying
+    iterator.
+    */
+    static iteration_proxy<iterator> iterator_wrapper(reference cont)
+    {
+        return iteration_proxy<iterator>(cont);
+    }
+
+    /*!
+    @copydoc iterator_wrapper(reference)
+    */
+    static iteration_proxy<const_iterator> iterator_wrapper(const_reference cont)
+    {
+        return iteration_proxy<const_iterator>(cont);
+    }
+
+
   private:
     //////////////////////
     // lexer and parser //

src/json.hpp.re2c

@@ -6152,43 +6152,35 @@ class basic_json
         }
     };
 
-    /*!
-    @brief wrapper to access iterator member functions in range-based for
 
-    This class allows to access @ref iterator::key() and @ref iterator::value()
+  private:
-    during range-based for loops. In these loops, a reference to the JSON
+    /// proxy class for the iterator_wrapper functions
-    values is returned, so there is no access to the underlying iterator.
+    template<typename IteratorType>
-    */
+    class iteration_proxy
-    class iterator_wrapper
     {
       private:
-        /// the container to iterate
+        /// helper class for iteration
-        typename basic_json::reference container;
+        class iteration_proxy_internal
-        /// the type of the iterator to use while iteration
-        using json_iterator = decltype(std::begin(container));
-
-        /// internal iterator wrapper
-        class iterator_wrapper_internal
         {
           private:
             /// the iterator
-            json_iterator anchor;
+            IteratorType anchor;
             /// an index for arrays
             size_t array_index = 0;
 
           public:
-            /// construct wrapper given an iterator
+            iteration_proxy_internal(IteratorType it)
-            iterator_wrapper_internal(json_iterator i) : anchor(i)
+                : anchor(it)
             {}
 
             /// dereference operator (needed for range-based for)
-            iterator_wrapper_internal& operator*()
+            iteration_proxy_internal& operator*()
             {
                 return *this;
             }
 
             /// increment operator (needed for range-based for)
-            iterator_wrapper_internal& operator++()
+            iteration_proxy_internal& operator++()
             {
                 ++anchor;
                 ++array_index;
@@ -6197,7 +6189,7 @@ class basic_json
             }
 
             /// inequality operator (needed for range-based for)
-            bool operator!= (const iterator_wrapper_internal& o)
+            bool operator!= (const iteration_proxy_internal& o)
             {
                 return anchor != o.anchor;
             }
@@ -6228,31 +6220,57 @@ class basic_json
             }
 
             /// return value of the iterator
-            typename json_iterator::reference value() const
+            typename IteratorType::reference value() const
             {
                 return anchor.value();
             }
         };
 
+        /// the container to iterate
+        typename IteratorType::reference container;
+
       public:
-        /// construct iterator wrapper from a container
+        /// construct iteration proxy from a container
-        iterator_wrapper(typename basic_json::reference cont)
+        iteration_proxy(typename IteratorType::reference cont)
             : container(cont)
         {}
 
         /// return iterator begin (needed for range-based for)
-        iterator_wrapper_internal begin()
+        iteration_proxy_internal begin()
         {
-            return iterator_wrapper_internal(container.begin());
+            return iteration_proxy_internal(container.begin());
         }
 
         /// return iterator end (needed for range-based for)
-        iterator_wrapper_internal end()
+        iteration_proxy_internal end()
         {
-            return iterator_wrapper_internal(container.end());
+            return iteration_proxy_internal(container.end());
         }
     };
 
+  public:
+    /*!
+    @brief wrapper to access iterator member functions in range-based for
+
+    This functuion allows to access @ref iterator::key() and @ref
+    iterator::value() during range-based for loops. In these loops, a reference
+    to the JSON values is returned, so there is no access to the underlying
+    iterator.
+    */
+    static iteration_proxy<iterator> iterator_wrapper(reference cont)
+    {
+        return iteration_proxy<iterator>(cont);
+    }
+
+    /*!
+    @copydoc iterator_wrapper(reference)
+    */
+    static iteration_proxy<const_iterator> iterator_wrapper(const_reference cont)
+    {
+        return iteration_proxy<const_iterator>(cont);
+    }
+
+
   private:
     //////////////////////
     // lexer and parser //

test/unit.cpp

@@ -9653,6 +9653,141 @@ TEST_CASE("iterator_wrapper")
         }
     }
 
+    SECTION("const object")
+    {
+        SECTION("value")
+        {
+            const json j = {{"A", 1}, {"B", 2}};
+            int counter = 1;
+
+            for (auto i : json::iterator_wrapper(j))
+            {
+                switch (counter++)
+                {
+                    case 1:
+                    {
+                        CHECK(i.key() == "A");
+                        CHECK(i.value() == json(1));
+                        break;
+                    }
+
+                    case 2:
+                    {
+                        CHECK(i.key() == "B");
+                        CHECK(i.value() == json(2));
+                        break;
+                    }
+
+                    default:
+                    {
+                        break;
+                    }
+                }
+            }
+
+            CHECK(counter == 3);
+        }
+
+        SECTION("reference")
+        {
+            const json j = {{"A", 1}, {"B", 2}};
+            int counter = 1;
+
+            for (auto& i : json::iterator_wrapper(j))
+            {
+                switch (counter++)
+                {
+                    case 1:
+                    {
+                        CHECK(i.key() == "A");
+                        CHECK(i.value() == json(1));
+                        break;
+                    }
+
+                    case 2:
+                    {
+                        CHECK(i.key() == "B");
+                        CHECK(i.value() == json(2));
+                        break;
+                    }
+
+                    default:
+                    {
+                        break;
+                    }
+                }
+            }
+
+            CHECK(counter == 3);
+        }
+
+        SECTION("const value")
+        {
+            const json j = {{"A", 1}, {"B", 2}};
+            int counter = 1;
+
+            for (const auto i : json::iterator_wrapper(j))
+            {
+                switch (counter++)
+                {
+                    case 1:
+                    {
+                        CHECK(i.key() == "A");
+                        CHECK(i.value() == json(1));
+                        break;
+                    }
+
+                    case 2:
+                    {
+                        CHECK(i.key() == "B");
+                        CHECK(i.value() == json(2));
+                        break;
+                    }
+
+                    default:
+                    {
+                        break;
+                    }
+                }
+            }
+
+            CHECK(counter == 3);
+        }
+
+        SECTION("const reference")
+        {
+            const json j = {{"A", 1}, {"B", 2}};
+            int counter = 1;
+
+            for (const auto& i : json::iterator_wrapper(j))
+            {
+                switch (counter++)
+                {
+                    case 1:
+                    {
+                        CHECK(i.key() == "A");
+                        CHECK(i.value() == json(1));
+                        break;
+                    }
+
+                    case 2:
+                    {
+                        CHECK(i.key() == "B");
+                        CHECK(i.value() == json(2));
+                        break;
+                    }
+
+                    default:
+                    {
+                        break;
+                    }
+                }
+            }
+
+            CHECK(counter == 3);
+        }
+    }
+
     SECTION("array")
     {
         SECTION("value")
@@ -9799,6 +9934,141 @@ TEST_CASE("iterator_wrapper")
         }
     }
 
+    SECTION("const array")
+    {
+        SECTION("value")
+        {
+            const json j = {"A", "B"};
+            int counter = 1;
+
+            for (auto i : json::iterator_wrapper(j))
+            {
+                switch (counter++)
+                {
+                    case 1:
+                    {
+                        CHECK(i.key() == "0");
+                        CHECK(i.value() == "A");
+                        break;
+                    }
+
+                    case 2:
+                    {
+                        CHECK(i.key() == "1");
+                        CHECK(i.value() == "B");
+                        break;
+                    }
+
+                    default:
+                    {
+                        break;
+                    }
+                }
+            }
+
+            CHECK(counter == 3);
+        }
+
+        SECTION("reference")
+        {
+            const json j = {"A", "B"};
+            int counter = 1;
+
+            for (auto& i : json::iterator_wrapper(j))
+            {
+                switch (counter++)
+                {
+                    case 1:
+                    {
+                        CHECK(i.key() == "0");
+                        CHECK(i.value() == "A");
+                        break;
+                    }
+
+                    case 2:
+                    {
+                        CHECK(i.key() == "1");
+                        CHECK(i.value() == "B");
+                        break;
+                    }
+
+                    default:
+                    {
+                        break;
+                    }
+                }
+            }
+
+            CHECK(counter == 3);
+        }
+
+        SECTION("const value")
+        {
+            const json j = {"A", "B"};
+            int counter = 1;
+
+            for (const auto i : json::iterator_wrapper(j))
+            {
+                switch (counter++)
+                {
+                    case 1:
+                    {
+                        CHECK(i.key() == "0");
+                        CHECK(i.value() == "A");
+                        break;
+                    }
+
+                    case 2:
+                    {
+                        CHECK(i.key() == "1");
+                        CHECK(i.value() == "B");
+                        break;
+                    }
+
+                    default:
+                    {
+                        break;
+                    }
+                }
+            }
+
+            CHECK(counter == 3);
+        }
+
+        SECTION("const reference")
+        {
+            const json j = {"A", "B"};
+            int counter = 1;
+
+            for (const auto& i : json::iterator_wrapper(j))
+            {
+                switch (counter++)
+                {
+                    case 1:
+                    {
+                        CHECK(i.key() == "0");
+                        CHECK(i.value() == "A");
+                        break;
+                    }
+
+                    case 2:
+                    {
+                        CHECK(i.key() == "1");
+                        CHECK(i.value() == "B");
+                        break;
+                    }
+
+                    default:
+                    {
+                        break;
+                    }
+                }
+            }
+
+            CHECK(counter == 3);
+        }
+    }
+
     SECTION("primitive")
     {
         SECTION("value")
@@ -9826,9 +10096,15 @@ TEST_CASE("iterator_wrapper")
                 ++counter;
                 CHECK(i.key() == "");
                 CHECK(i.value() == json(1));
+
+                // change value
+                i.value() = json(2);
             }
 
             CHECK(counter == 2);
+
+            // check if value has changed
+            CHECK(j == json(2));
         }
 
         SECTION("const value")
@@ -9846,7 +10122,7 @@ TEST_CASE("iterator_wrapper")
             CHECK(counter == 2);
         }
 
-        SECTION("reference")
+        SECTION("const reference")
         {
             json j = 1;
             int counter = 1;
@@ -9861,6 +10137,69 @@ TEST_CASE("iterator_wrapper")
             CHECK(counter == 2);
         }
     }
+
+    SECTION("const primitive")
+    {
+        SECTION("value")
+        {
+            const json j = 1;
+            int counter = 1;
+
+            for (auto i : json::iterator_wrapper(j))
+            {
+                ++counter;
+                CHECK(i.key() == "");
+                CHECK(i.value() == json(1));
+            }
+
+            CHECK(counter == 2);
+        }
+
+        SECTION("reference")
+        {
+            const json j = 1;
+            int counter = 1;
+
+            for (auto& i : json::iterator_wrapper(j))
+            {
+                ++counter;
+                CHECK(i.key() == "");
+                CHECK(i.value() == json(1));
+            }
+
+            CHECK(counter == 2);
+        }
+
+        SECTION("const value")
+        {
+            const json j = 1;
+            int counter = 1;
+
+            for (const auto i : json::iterator_wrapper(j))
+            {
+                ++counter;
+                CHECK(i.key() == "");
+                CHECK(i.value() == json(1));
+            }
+
+            CHECK(counter == 2);
+        }
+
+        SECTION("const reference")
+        {
+            const json j = 1;
+            int counter = 1;
+
+            for (const auto& i : json::iterator_wrapper(j))
+            {
+                ++counter;
+                CHECK(i.key() == "");
+                CHECK(i.value() == json(1));
+            }
+
+            CHECK(counter == 2);
+        }
+    }
 }
 
 TEST_CASE("compliance tests from json.org")