Add extra operator[] overload templates to address issue nlohmann#171

src/json.hpp

@@ -3272,8 +3272,6 @@ class basic_json
     the object and filled with a `null` value to make `key` a valid reference.
     In case the value was `null` before, it is converted to an object.
 
-    @note This function is required for compatibility reasons with Clang.
-
     @param[in] key  key of the element to access
 
     @return reference to the element at key @a key
@@ -3293,7 +3291,75 @@ class basic_json
     @since version 1.0.0
     */
     template<typename T, std::size_t n>
-    reference operator[](const T (&key)[n])
+    reference operator[](T* (&key)[n])
+    {
+        return operator[](static_cast<const T>(key));
+    }
+
+    /*!
+    @brief read-only access specified object element
+
+    Returns a const reference to the element at with specified key @a key. No
+    bounds checking is performed.
+
+    @warning If the element with key @a key does not exist, the behavior is
+    undefined.
+
+    @note This function is required for compatibility reasons with Clang.
+
+    @param[in] key  key of the element to access
+
+    @return const reference to the element at key @a key
+
+    @throw std::domain_error if JSON is not an object; example: `"cannot use
+    operator[] with null"`
+
+    @complexity Logarithmic in the size of the container.
+
+    @liveexample{The example below shows how object elements can be read using
+    the [] operator.,operatorarray__key_type_const}
+
+    @sa @ref at(const typename object_t::key_type&) for access by reference
+    with range checking
+    @sa @ref value() for access by value with a default value
+
+    @since version 1.0.0
+    */
+    template<typename T, std::size_t n>
+    const_reference operator[](T* (&key)[n]) const
+    {
+        return operator[](static_cast<const T>(key));
+    }
+
+    /*!
+    @brief access specified object element
+
+    Returns a reference to the element at with specified key @a key.
+
+    @note If @a key is not found in the object, then it is silently added to
+    the object and filled with a `null` value to make `key` a valid reference.
+    In case the value was `null` before, it is converted to an object.
+
+    @param[in] key  key of the element to access
+
+    @return reference to the element at key @a key
+
+    @throw std::domain_error if JSON is not an object or null; example:
+    `"cannot use operator[] with null"`
+
+    @complexity Logarithmic in the size of the container.
+
+    @liveexample{The example below shows how object elements can be read and
+    written using the [] operator.,operatorarray__key_type}
+
+    @sa @ref at(const typename object_t::key_type&) for access by reference
+    with range checking
+    @sa @ref value() for access by value with a default value
+
+    @since version 2.0.0
+    */
+    template<typename T>
+    reference operator[](T* key)
     {
         // implicitly convert null to object
         if (is_null())
@@ -3323,8 +3389,6 @@ class basic_json
     @warning If the element with key @a key does not exist, the behavior is
     undefined.
 
-    @note This function is required for compatibility reasons with Clang.
-
     @param[in] key  key of the element to access
 
     @return const reference to the element at key @a key
@@ -3341,10 +3405,10 @@ class basic_json
     with range checking
     @sa @ref value() for access by value with a default value
 
-    @since version 1.0.0
+    @since version 2.0.0
     */
-    template<typename T, std::size_t n>
-    const_reference operator[](const T (&key)[n]) const
+    template<typename T>
+    const_reference operator[](T* key) const
     {
         // at only works for objects
         if (is_object())

src/json.hpp.re2c

@@ -3272,8 +3272,6 @@ class basic_json
     the object and filled with a `null` value to make `key` a valid reference.
     In case the value was `null` before, it is converted to an object.
 
-    @note This function is required for compatibility reasons with Clang.
-
     @param[in] key  key of the element to access
 
     @return reference to the element at key @a key
@@ -3293,7 +3291,75 @@ class basic_json
     @since version 1.0.0
     */
     template<typename T, std::size_t n>
-    reference operator[](const T (&key)[n])
+    reference operator[](T* (&key)[n])
+    {
+        return operator[](static_cast<const T>(key));
+    }
+
+    /*!
+    @brief read-only access specified object element
+
+    Returns a const reference to the element at with specified key @a key. No
+    bounds checking is performed.
+
+    @warning If the element with key @a key does not exist, the behavior is
+    undefined.
+
+    @note This function is required for compatibility reasons with Clang.
+
+    @param[in] key  key of the element to access
+
+    @return const reference to the element at key @a key
+
+    @throw std::domain_error if JSON is not an object; example: `"cannot use
+    operator[] with null"`
+
+    @complexity Logarithmic in the size of the container.
+
+    @liveexample{The example below shows how object elements can be read using
+    the [] operator.,operatorarray__key_type_const}
+
+    @sa @ref at(const typename object_t::key_type&) for access by reference
+    with range checking
+    @sa @ref value() for access by value with a default value
+
+    @since version 1.0.0
+    */
+    template<typename T, std::size_t n>
+    const_reference operator[](T* (&key)[n]) const
+    {
+        return operator[](static_cast<const T>(key));
+    }
+
+    /*!
+    @brief access specified object element
+
+    Returns a reference to the element at with specified key @a key.
+
+    @note If @a key is not found in the object, then it is silently added to
+    the object and filled with a `null` value to make `key` a valid reference.
+    In case the value was `null` before, it is converted to an object.
+
+    @param[in] key  key of the element to access
+
+    @return reference to the element at key @a key
+
+    @throw std::domain_error if JSON is not an object or null; example:
+    `"cannot use operator[] with null"`
+
+    @complexity Logarithmic in the size of the container.
+
+    @liveexample{The example below shows how object elements can be read and
+    written using the [] operator.,operatorarray__key_type}
+
+    @sa @ref at(const typename object_t::key_type&) for access by reference
+    with range checking
+    @sa @ref value() for access by value with a default value
+
+    @since version 2.0.0
+    */
+    template<typename T>
+    reference operator[](T* key)
     {
         // implicitly convert null to object
         if (is_null())
@@ -3323,8 +3389,6 @@ class basic_json
     @warning If the element with key @a key does not exist, the behavior is
     undefined.
 
-    @note This function is required for compatibility reasons with Clang.
-
     @param[in] key  key of the element to access
 
     @return const reference to the element at key @a key
@@ -3341,10 +3405,10 @@ class basic_json
     with range checking
     @sa @ref value() for access by value with a default value
 
-    @since version 1.0.0
+    @since version 2.0.0
     */
-    template<typename T, std::size_t n>
-    const_reference operator[](const T (&key)[n]) const
+    template<typename T>
+    const_reference operator[](T* key) const
     {
         // at only works for objects
         if (is_object())

test/unit.cpp

@@ -12201,5 +12201,54 @@ TEST_CASE("regression tests")
     {
         CHECK(json::parse("\"\\ud80c\\udc60abc\"").get<json::string_t>() == u8"\U00013060abc");
     }
+
+
+    SECTION("issue #144 - Cannot index by key of type static constexpr const char*")
+    {
+        json j;
+
+        // Non-const access with key as "char []"
+        char array_key[] = "Key1";
+        CHECK_NOTHROW(j[array_key] = 1);
+        CHECK(j[array_key] == json(1));
+
+        // Non-const access with key as "const char[]"
+        const char const_array_key[] = "Key2";
+        CHECK_NOTHROW(j[const_array_key] = 2);
+        CHECK(j[const_array_key] == json(2));
+
+        // Non-const access with key as "char *"
+        char _ptr_key[] = "Key3";
+        char * ptr_key = &_ptr_key[0];
+        CHECK_NOTHROW(j[ptr_key] = 3);
+        CHECK(j[ptr_key] == json(3));
+
+        // Non-const access with key as "const char *"
+        const char * const_ptr_key = "Key4";
+        CHECK_NOTHROW(j[const_ptr_key] = 4);
+        CHECK(j[const_ptr_key] == json(4));
+
+        // Non-const access with key as "static constexpr const char *"
+        static constexpr const char* constexpr_ptr_key = "Key5";
+        CHECK_NOTHROW(j[constexpr_ptr_key] = 5);
+        CHECK(j[constexpr_ptr_key] == json(5));
+
+        const json j_const = j;
+
+        // Non-const access with key as "char []"
+        CHECK(j_const[array_key] == json(1));
+
+        // Non-const access with key as "const char[]"
+        CHECK(j_const[const_array_key] == json(2));
+
+        // Non-const access with key as "char *"
+        CHECK(j_const[ptr_key] == json(3));
+
+        // Non-const access with key as "const char *"
+        CHECK(j_const[const_ptr_key] == json(4));
+
+        // Non-const access with key as "static constexpr const char *"
+        CHECK(j_const[constexpr_ptr_key] == json(5));
+    }
 }