extended "add" to cope with arrays

src/json.hpp

@@ -9560,7 +9560,25 @@ basic_json_parser_63:
                     throw std::domain_error("'add' operation must have member 'value'");
                 }
 
-                result[ptr] = it_value->second;
+                const auto last_path = ptr.pop_back();
+                basic_json& parent = result.at(ptr);
+
+                if (parent.is_object())
+                {
+                    parent[last_path] = it_value->second;
+                }
+                else if (parent.is_array())
+                {
+                    if (last_path == "-")
+                    {
+                        parent.push_back(it_value->second);
+                    }
+                    else
+                    {
+                        parent.insert(parent.begin() + std::stoi(last_path),
+                                      it_value->second);
+                    }
+                }
             }
             else if (op == "remove")
             {

src/json.hpp.re2c

@@ -8870,7 +8870,25 @@ class basic_json
                     throw std::domain_error("'add' operation must have member 'value'");
                 }
 
-                result[ptr] = it_value->second;
+                const auto last_path = ptr.pop_back();
+                basic_json& parent = result.at(ptr);
+
+                if (parent.is_object())
+                {
+                    parent[last_path] = it_value->second;
+                }
+                else if (parent.is_array())
+                {
+                    if (last_path == "-")
+                    {
+                        parent.push_back(it_value->second);
+                    }
+                    else
+                    {
+                        parent.insert(parent.begin() + std::stoi(last_path),
+                                      it_value->second);
+                    }
+                }
             }
             else if (op == "remove")
             {

test/unit.cpp

@@ -12421,6 +12421,29 @@ TEST_CASE("JSON patch")
             CHECK(doc.apply_patch(patch) == expected);
         }
 
+        SECTION("example A.2 - Adding an Array Element")
+        {
+            // An example target JSON document:
+            json doc = R"(
+                { "foo": [ "bar", "baz" ] }
+            )"_json;
+
+            // A JSON Patch document:
+            json patch = R"(
+                [
+                    { "op": "add", "path": "/foo/1", "value": "qux" }
+                ]
+            )"_json;
+
+            // The resulting JSON document:
+            json expected = R"(
+                { "foo": [ "bar", "qux", "baz" ] }
+            )"_json;
+
+            // check if patched value is as expected
+            CHECK(doc.apply_patch(patch) == expected);
+        }
+
         SECTION("example A.3 - Removing an Object Member")
         {
             // An example target JSON document:
@@ -12616,9 +12639,12 @@ TEST_CASE("JSON patch")
             // an existing object, nor a member of an existing array.
 
             CHECK_THROWS_AS(doc.apply_patch(patch), std::out_of_range);
-            CHECK_THROWS_WITH(doc.apply_patch(patch), "unresolved reference token 'bat'");
+            CHECK_THROWS_WITH(doc.apply_patch(patch), "key 'baz' not found");
         }
 
+        // A.13.  Invalid JSON Patch Document
+        // not applicable
+
         SECTION("example A.14 - Escape Ordering")
         {
             // An example target JSON document: