From a645a766e4f523274da9f02979efaf556c3af04c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Th=C3=A9o=20DELRIEU?= <theo@tanker.io>
Date: Tue, 29 Nov 2016 13:09:51 +0100
Subject: [PATCH] add support for non-default-constructible udt

---
 src/json.hpp          | 139 +++++++-----
 test/src/unit-udt.cpp | 486 +++++++-----------------------------------
 2 files changed, 162 insertions(+), 463 deletions(-)

diff --git a/src/json.hpp b/src/json.hpp
index f63b72f48..edf8a78eb 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -275,14 +275,32 @@ struct is_compatible_basic_json_type
 };
 
 
-// This trait checks if JSONSerializer<T>::from_json exists
+// This trait checks if JSONSerializer<T>::from_json(json const&, udt&) exists
 template <template <typename, typename> class JSONSerializer, typename Json,
           typename T>
 struct has_from_json
 {
 private:
-  template <typename U, typename = decltype(uncvref_t<U>::from_json(
-                            std::declval<Json>(), std::declval<T &>()))>
+  // also check the return type of from_json
+  template <typename U, typename = enable_if_t<std::is_same<void, decltype(uncvref_t<U>::from_json(
+                            std::declval<Json>(), std::declval<T &>()))>::value>>
+  static int detect(U &&);
+
+  static void detect(...);
+
+public:
+  static constexpr bool value = std::is_integral<decltype(
+      detect(std::declval<JSONSerializer<T, void>>()))>::value;
+};
+
+// This trait checks if JSONSerializer<T>::from_json(json const&) exists
+// this overload is used for non-default-constructible user-defined-types
+template <template <typename, typename> class JSONSerializer, typename Json,
+          typename T>
+struct has_non_default_from_json
+{
+private:
+  template <typename U, typename = enable_if_t<std::is_same<T, decltype(uncvref_t<U>::from_json(std::declval<Json>()))>::value>>
   static int detect(U &&);
 
   static void detect(...);
@@ -311,8 +329,8 @@ public:
 
 // those declarations are needed to workaround a MSVC bug related to ADL
 // (taken from MSVC-Ranges implementation)
-void to_json();
-void from_json();
+//void to_json();
+//void from_json();
 
 struct to_json_fn
 {
@@ -2376,57 +2394,63 @@ class basic_json
         return *this;
     }
 
-    /*!
-    @brief destructor
-
-    Destroys the JSON value and frees all allocated memory.
-
-    @complexity Linear.
-
-    @requirement This function helps `basic_json` satisfying the
-    [Container](http://en.cppreference.com/w/cpp/concept/Container)
-    requirements:
-    - The complexity is linear.
-    - All stored elements are destroyed and all memory is freed.
-
-    @since version 1.0.0
-    */
-    ~basic_json()
+    // this overload is needed, since constructor for udt is explicit
+    template <typename T, enable_if_t<not detail::is_compatible_basic_json_type<
+                                          uncvref_t<T>, basic_json_t>::value and
+                                      detail::has_to_json<JSONSerializer, basic_json_t, uncvref_t<T>>::value>>
+    reference &operator=(T &&val) noexcept(std::is_nothrow_constructible<basic_json_t, uncvref_t<T>>::value and
+                                           std::is_nothrow_move_assignable<uncvref_t<T>>::value)
     {
-        assert_invariant();
+      static_assert(sizeof(T) == 0 , "");
+      // I'm not sure this a is good practice...
+      return *this = basic_json_t{std::forward<T>(val)};
+    }
 
-        switch (m_type)
-        {
-            case value_t::object:
-            {
-                AllocatorType<object_t> alloc;
-                alloc.destroy(m_value.object);
-                alloc.deallocate(m_value.object, 1);
-                break;
-            }
+        /*!
+        @brief destructor
 
-            case value_t::array:
-            {
-                AllocatorType<array_t> alloc;
-                alloc.destroy(m_value.array);
-                alloc.deallocate(m_value.array, 1);
-                break;
-            }
+        Destroys the JSON value and frees all allocated memory.
 
-            case value_t::string:
-            {
-                AllocatorType<string_t> alloc;
-                alloc.destroy(m_value.string);
-                alloc.deallocate(m_value.string, 1);
-                break;
-            }
+        @complexity Linear.
 
-            default:
-            {
-                // all other types need no specific destructor
-                break;
-            }
-        }
+        @requirement This function helps `basic_json` satisfying the
+        [Container](http://en.cppreference.com/w/cpp/concept/Container)
+        requirements:
+        - The complexity is linear.
+        - All stored elements are destroyed and all memory is freed.
+
+        @since version 1.0.0
+        */
+        ~basic_json() {
+      assert_invariant();
+
+      switch (m_type) {
+      case value_t::object: {
+        AllocatorType<object_t> alloc;
+        alloc.destroy(m_value.object);
+        alloc.deallocate(m_value.object, 1);
+        break;
+      }
+
+      case value_t::array: {
+        AllocatorType<array_t> alloc;
+        alloc.destroy(m_value.array);
+        alloc.deallocate(m_value.array, 1);
+        break;
+      }
+
+      case value_t::string: {
+        AllocatorType<string_t> alloc;
+        alloc.destroy(m_value.string);
+        alloc.deallocate(m_value.string, 1);
+        break;
+      }
+
+      default: {
+        // all other types need no specific destructor
+        break;
+      }
+      }
     }
 
     /// @}
@@ -3191,6 +3215,19 @@ class basic_json
       return ret;
     }
 
+    // This overload is chosen for non-default constructible user-defined-types
+    template <
+        typename T,
+        enable_if_t<not detail::is_compatible_basic_json_type<
+                        T, basic_json_t>::value and
+                        detail::has_non_default_from_json<JSONSerializer, basic_json_t,
+                                              T>::value,
+                    short> = 0>
+    T get() const
+    {
+      return JSONSerializer<T>::from_json(*this);
+    }
+
     /*!
     @brief get a pointer value (explicit)
 
diff --git a/test/src/unit-udt.cpp b/test/src/unit-udt.cpp
index 800f9868e..cd9ec1c46 100644
--- a/test/src/unit-udt.cpp
+++ b/test/src/unit-udt.cpp
@@ -26,443 +26,105 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
+#include <array>
 #include <string>
 #include <memory>
 #include "catch.hpp"
 
 #include "json.hpp"
-using nlohmann::json;
 
 namespace udt
 {
-struct empty_type {};
-struct pod_type {
-  int a;
-  char b;
-  short c;
-};
-
-struct bit_more_complex_type {
-  pod_type a;
-  pod_type b;
-  std::string c;
-};
-
-// best optional implementation ever
-template <typename T>
-class optional_type
-{
-public:
-  optional_type() = default;
-  explicit optional_type(T val) : _val(std::make_shared<T>(std::move(val))) {}
-  explicit operator bool() const noexcept { return _val != nullptr; }
-
-  T const &operator*() const { return *_val; }
-  optional_type& operator=(T const& t)
+  struct age
   {
-    _val = std::make_shared<T>(t);
-    return *this;
-  }
+    int val;
+  };
 
-private:
-  std::shared_ptr<T> _val;
-};
+  struct name
+  {
+    std::string val;
+  };
 
-// free to/from_json functions
+  struct address
+  {
+    std::string val;
+  };
 
-void to_json(json& j, empty_type)
-{
-  j = json::object();
+  struct person
+  {
+    age age;
+    name name;
+  };
+
+  struct contact
+  {
+    person person;
+    address address;
+  };
+
+  struct contact_book
+  {
+    name book_name;
+    std::vector<contact> contacts;
+  };
 }
 
-void to_json(json& j, pod_type const& p)
-{
-  j = json{{"a", p.a}, {"b", p.b}, {"c", p.c}};
-}
-
-void to_json(json& j, bit_more_complex_type const& p)
-{
-  j = json{{"a", json(p.a)}, {"b", json(p.b)}, {"c", p.c}};
-}
-
-template <typename T>
-void to_json(json& j, optional_type<T> const& opt)
-{
-  if (!opt)
-    j = nullptr;
-  else
-    j = json(*opt);
-}
-
-void from_json(json const& j, empty_type& t)
-{
-  assert(j.empty());
-  t = empty_type{};
-}
-
-void from_json(json const&j, pod_type& t)
-{
-  t = {j["a"].get<int>(), j["b"].get<char>(), j["c"].get<short>()};
-}
-
-void from_json(json const&j, bit_more_complex_type& t)
-{
-   // relying on json_traits struct here..
-   t = {j["a"].get<udt::pod_type>(), j["b"].get<udt::pod_type>(),
-        j["c"].get<std::string>()};
-}
-
-template <typename T>
-void from_json(json const& j, optional_type<T>& t)
-{
-  if (j.is_null())
-    t = optional_type<T>{};
-  else
-    t = j.get<T>();
-}
-
-inline bool operator==(pod_type const& lhs, pod_type const& rhs) noexcept
-{
-  return std::tie(lhs.a, lhs.b, lhs.c) == std::tie(rhs.a, rhs.b, rhs.c);
-}
-
-inline bool operator==(bit_more_complex_type const &lhs,
-                       bit_more_complex_type const &rhs) noexcept {
-  return std::tie(lhs.a, lhs.b, lhs.c) == std::tie(rhs.a, rhs.b, rhs.c);
-}
-
-template <typename T>
-inline bool operator==(optional_type<T> const& lhs, optional_type<T> const& rhs)
-{
-  if (!lhs && !rhs)
-    return true;
-  if (!lhs || !rhs)
-    return false;
-  return *lhs == *rhs;
-}
-}
-
-TEST_CASE("constructors for user-defined types", "[udt]")
-{
-  SECTION("empty type")
-  {
-    udt::empty_type const e{};
-    auto const j = json{e};
-    auto k = json::object();
-    CHECK(j == k);
-  }
-
-  SECTION("pod type")
-  {
-    auto const e = udt::pod_type{42, 42, 42};
-    auto j = json{e};
-    auto k = json{{"a", 42}, {"b", 42}, {"c", 42}};
-    CHECK(j == k);
-  }
-
-  SECTION("bit more complex type")
-  {
-    auto const e =
-        udt::bit_more_complex_type{{42, 42, 42}, {41, 41, 41}, "forty"};
-
-    auto j = json{e};
-    auto k = json{{"a", {{"a", 42}, {"b", 42}, {"c", 42}}},
-                  {"b", {{"a", 41}, {"b", 41}, {"c", 41}}},
-                  {"c", "forty"}};
-    CHECK(j == k);
-  }
-
-  SECTION("vector of udt")
-  {
-    std::vector<udt::bit_more_complex_type> v;
-    auto const e =
-        udt::bit_more_complex_type{{42, 42, 42}, {41, 41, 41}, "forty"};
-
-    v.emplace_back(e);
-    v.emplace_back(e);
-    v.emplace_back(e);
-
-    json j = v;
-    auto k = json{{"a", {{"a", 42}, {"b", 42}, {"c", 42}}},
-                  {"b", {{"a", 41}, {"b", 41}, {"c", 41}}},
-                  {"c", "forty"}};
-    auto l = json{k, k, k};
-    CHECK(j == l);
-  }
-
-  SECTION("optional type") {
-    SECTION("regular case") {
-      udt::optional_type<int> u{3};
-      CHECK(json{u} == json(3));
-    }
-
-    SECTION("nullopt case") {
-      udt::optional_type<float> v;
-      CHECK(json{v} == json{});
-    }
-
-    SECTION("optional of json convertible type")
-    {
-      auto const e =
-          udt::bit_more_complex_type{{42, 42, 42}, {41, 41, 41}, "forty"};
-      udt::optional_type<udt::bit_more_complex_type> o{e};
-      auto k = json{{"a", {{"a", 42}, {"b", 42}, {"c", 42}}},
-                    {"b", {{"a", 41}, {"b", 41}, {"c", 41}}},
-                    {"c", "forty"}};
-      CHECK(json{o} == k);
-    }
-
-    SECTION("optional of vector of json convertible type")
-    {
-      std::vector<udt::bit_more_complex_type> v;
-      auto const e =
-          udt::bit_more_complex_type{{42, 42, 42}, {41, 41, 41}, "forty"};
-      v.emplace_back(e);
-      v.emplace_back(e);
-      v.emplace_back(e);
-      udt::optional_type<std::vector<udt::bit_more_complex_type>> o{v};
-      auto k = json{{"a", {{"a", 42}, {"b", 42}, {"c", 42}}},
-                    {"b", {{"a", 41}, {"b", 41}, {"c", 41}}},
-                    {"c", "forty"}};
-      auto l = json{k, k, k};
-      CHECK(json{o} == l);
-    }
-  }
-}
-
-TEST_CASE("get<> for user-defined types", "[udt]")
-{
-  SECTION("pod type")
-  {
-    auto const e = udt::pod_type{42, 42, 42};
-    auto const j = json{{"a", 42}, {"b", 42}, {"c", 42}};
-
-    auto const obj = j.get<udt::pod_type>();
-    CHECK(e == obj);
-  }
-
-  SECTION("bit more complex type")
-  {
-    auto const e =
-        udt::bit_more_complex_type{{42, 42, 42}, {41, 41, 41}, "forty"};
-    auto const j = json{{"a", {{"a", 42}, {"b", 42}, {"c", 42}}},
-                        {"b", {{"a", 41}, {"b", 41}, {"c", 41}}},
-                        {"c", "forty"}};
-
-    auto const obj = j.get<udt::bit_more_complex_type>();
-    CHECK(e == obj);
-  }
-
-  SECTION("vector of udt")
-  {
-    auto const e =
-        udt::bit_more_complex_type{{42, 42, 42}, {41, 41, 41}, "forty"};
-    std::vector<udt::bit_more_complex_type> v{e, e, e};
-    auto const j = json(v);
-
-    auto const obj = j.get<decltype(v)>();
-    CHECK(v == obj);
-  }
-
-  SECTION("optional")
-  {
-    SECTION("from null")
-    {
-      udt::optional_type<int> o;
-      json j;
-      CHECK(j.get<decltype(o)>() == o);
-    }
-
-    SECTION("from value")
-    {
-      json j{{"a", 42}, {"b", 42}, {"c", 42}};
-      auto v = j.get<udt::optional_type<udt::pod_type>>();
-      auto expected = udt::pod_type{42,42,42};
-      REQUIRE(v);
-      CHECK(*v == expected);
-    }
-  }
-}
-
-TEST_CASE("to_json free function", "[udt]")
-{
-  SECTION("pod_type")
-  {
-    auto const e = udt::pod_type{42, 42, 42};
-    auto const expected = json{{"a", 42}, {"b", 42}, {"c", 42}};
-
-    json j;
-    nlohmann::to_json(j, e);
-    CHECK(j == expected);
-  }
-
-  SECTION("bit_more_complex_type")
-  {
-    auto const e =
-        udt::bit_more_complex_type{{42, 42, 42}, {41, 41, 41}, "forty"};
-    auto const expected = json{{"a", {{"a", 42}, {"b", 42}, {"c", 42}}},
-                        {"b", {{"a", 41}, {"b", 41}, {"c", 41}}},
-                        {"c", "forty"}};
-    json j;
-    nlohmann::to_json(j, e);
-    CHECK(j == expected);
-  }
-
-  SECTION("optional_type")
-  {
-    SECTION("from null")
-    {
-      udt::optional_type<udt::pod_type> o;
-
-      json expected;
-      json j;
-      nlohmann::to_json(j, o);
-      CHECK(expected == j);
-    }
-
-    SECTION("from value")
-    {
-      udt::optional_type<udt::pod_type> o{{42, 42, 42}};
-
-      auto const expected = json{{"a", 42}, {"b", 42}, {"c", 42}};
-      json j;
-      nlohmann::to_json(j, o);
-      CHECK(expected == j);
-    }
-  }
-}
-
-TEST_CASE("from_json free function", "[udt]")
-{
-  SECTION("pod_type")
-  {
-    auto const expected = udt::pod_type{42, 42, 42};
-    auto const j = json{{"a", 42}, {"b", 42}, {"c", 42}};
-
-    udt::pod_type p;
-    nlohmann::from_json(j, p);
-    CHECK(p == expected);
-  }
-
-  SECTION("bit_more_complex_type")
-  {
-    auto const expected =
-        udt::bit_more_complex_type{{42, 42, 42}, {41, 41, 41}, "forty"};
-    auto const j = json{{"a", {{"a", 42}, {"b", 42}, {"c", 42}}},
-                        {"b", {{"a", 41}, {"b", 41}, {"c", 41}}},
-                        {"c", "forty"}};
-    udt::bit_more_complex_type p;
-    nlohmann::from_json(j, p);
-    CHECK(p == expected);
-  }
-
-  SECTION("optional_type")
-  {
-    SECTION("from null")
-    {
-      udt::optional_type<udt::pod_type> expected;
-      json j;
-      udt::optional_type<udt::pod_type> o;
-
-      nlohmann::from_json(j, o);
-      CHECK(expected == o);
-    }
-
-    SECTION("from value")
-    {
-      udt::optional_type<udt::pod_type> expected{{42, 42, 42}};
-      auto const j = json{{"a", 42}, {"b", 42}, {"c", 42}};
-      udt::optional_type<udt::pod_type> o;
-
-      nlohmann::from_json(j, o);
-      CHECK(expected == o);
-    }
-  }
-}
-
-// custom serializer, uses adl by default
-template <typename T, typename = void>
-struct my_serializer
-{
-  template <typename Json>
-  static void from_json(Json const& j, T& val)
-  {
-    nlohmann::from_json(j, val);
-  }
-
-  template <typename Json>
-  static void to_json(Json& j, T const& val)
-  {
-    nlohmann::to_json(j, val);
-  }
-};
-
-// partial specialization on optional_type
-template <typename T>
-struct my_serializer<udt::optional_type<T>>
-{
-  template <typename Json>
-  static void from_json(Json const& j, udt::optional_type<T>& opt)
-  {
-    if (j.is_null())
-      opt = nullptr;
-    else
-      opt = j.get<T>();
-  }
-
-  template <typename Json>
-  static void to_json(Json& j, udt::optional_type<T> const& opt)
-  {
-    if (opt)
-      j = *opt;
-    else
-      j = nullptr;
-  }
-};
-
-using my_json = nlohmann::basic_json<std::map, std::vector, std::string, bool,
-                                     std::int64_t, std::uint64_t, double,
-                                     std::allocator, my_serializer>;
-
+// to_json methods for default basic_json
 namespace udt
 {
-  void to_json(my_json& j, pod_type const& val)
+  void to_json(nlohmann::json& j, age a)
   {
-    j = my_json{{"a", val.a}, {"b", val.b}, {"c", val.c}};
+    j = a.val;
   }
 
-  void from_json(my_json const& j, pod_type& val)
+  void to_json(nlohmann::json& j, name const& n)
   {
-    val = {j["a"].get<int>(), j["b"].get<char>(), j["c"].get<short>()};
+    j = n.val;
+  }
+
+  void to_json(nlohmann::json& j, person const& p)
+  {
+    using nlohmann::json;
+    j = json{{"age", json{p.age}}, {"name", json{p.name}}};
+
+    // this unfortunately does not compile ...
+    // j["age"] = p.age;
+    // j["name"] = p.name;
+  }
+
+  void to_json(nlohmann::json& j, address const& a)
+  {
+    j = a.val;
+  }
+
+  void to_json(nlohmann::json& j, contact const& c)
+  {
+    using nlohmann::json;
+    j = json{{"person", json{c.person}}, {"address", json{c.address}}};
+  }
+
+  void to_json(nlohmann::json& j, contact_book const& cb)
+  {
+    using nlohmann::json;
+    j = json{{"name", json{cb.book_name}}, {"contacts", cb.contacts}};
   }
 }
 
-TEST_CASE("custom serializer", "[udt]")
+TEST_CASE("basic usage", "[udt]")
 {
-  SECTION("default use works like default serializer")
+  using nlohmann::json;
+
+  SECTION("conversion to json via free-functions")
   {
-    udt::pod_type pod{1, 2, 3};
-    auto const j = my_json{pod};
+    udt::age a{23};
 
-    auto const j2 = json{pod};
-    CHECK(j.dump() == j2.dump());
+    CHECK(json{a} == json{23});
 
-    auto const pod2 = j.get<udt::pod_type>();
-    auto const pod3 = j2.get<udt::pod_type>();
-    CHECK(pod2 == pod3);
-    CHECK(pod2 == pod);
+    // a bit narcissic maybe :) ?
+    udt::name n{"theo"};
+    CHECK(json{n} == json{"theo"});
+
+    udt::person sfinae_addict{a, n};
+    CHECK(json{sfinae_addict} == R"({"name":"theo", "age":23})"_json);
   }
-
-  SECTION("serializer specialization")
-  {
-    udt::optional_type<int> opt;
-
-    json j{opt};
-    CHECK(j.is_null());
-
-    opt = 42;
-    j = json{opt};
-    CHECK(j.get<udt::optional_type<int>>() == opt);
-    CHECK(42 == j.get<int>());
-  }
-}
+}
\ No newline at end of file