add implicit conversions test (operator T())

test/src/unit-udt.cpp

@@ -261,15 +261,19 @@ TEST_CASE("basic usage", "[udt]")
     {
         const auto big_json =
             u8R"({"name":"C++", "contacts" : [{"person" : {"age":23, "name":"theo", "country":"France"}, "address":"Paris"}, {"person" : {"age":42, "country":"中华人民共和国", "name":"王芳"}, "address":"Paris"}]})"_json;
+        SECTION("via explicit calls to get")
+        {
           const auto parsed_book = big_json.get<udt::contact_book>();
           const auto book_name = big_json["name"].get<udt::name>();
-        const auto contacts = big_json["contacts"].get<std::vector<udt::contact>>();
+          const auto contacts =
+              big_json["contacts"].get<std::vector<udt::contact>>();
           const auto contact_json = big_json["contacts"].at(0);
           const auto contact = contact_json.get<udt::contact>();
           const auto person = contact_json["person"].get<udt::person>();
           const auto address = contact_json["address"].get<udt::address>();
           const auto age = contact_json["person"]["age"].get<udt::age>();
-        const auto country = contact_json["person"]["country"].get<udt::country>();
+          const auto country =
+              contact_json["person"]["country"].get<udt::country>();
           const auto name = contact_json["person"]["name"].get<udt::name>();
 
           CHECK(age == a);
@@ -282,6 +286,31 @@ TEST_CASE("basic usage", "[udt]")
           CHECK(book_name == udt::name{"C++"});
           CHECK(book == parsed_book);
         }
+
+        SECTION("implicit conversions")
+        {
+          const udt::contact_book parsed_book = big_json;
+          const udt::name book_name = big_json["name"];
+          const std::vector<udt::contact> contacts = big_json["contacts"];
+          const auto contact_json = big_json["contacts"].at(0);
+          const udt::contact contact = contact_json;
+          const udt::person person = contact_json["person"];
+          const udt::address address = contact_json["address"];
+          const udt::age age = contact_json["person"]["age"];
+          const udt::country country = contact_json["person"]["country"];
+          const udt::name name = contact_json["person"]["name"];
+
+          CHECK(age == a);
+          CHECK(name == n);
+          CHECK(country == c);
+          CHECK(address == addr);
+          CHECK(person == sfinae_addict);
+          CHECK(contact == cpp_programmer);
+          CHECK(contacts == book.m_contacts);
+          CHECK(book_name == udt::name{"C++"});
+          CHECK(book == parsed_book);
+        }
+    }
 }
 
 namespace udt