Reference tuple from json (#5016)

* Add reference handling to tuples

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

* Remove template template type because pair isn't working

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

* amalgamate std::tie changes

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

* allow the elation of a move by removing the ref requirement

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

* force all number_xxx_t to be interchangeable

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

* Finally got amalgamate to work correctly

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

* remove const version, add a test case for scrambled number representations.

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

* Use the logical set of requirements instead of decltype because VS 2015 doesn't like it

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

---------

Signed-off-by: Evelyn LePain <ava.lepain@gmail.com>

include/nlohmann/detail/conversions/from_json.hpp

@@ -26,6 +26,7 @@
 #include <nlohmann/detail/meta/identity_tag.hpp>
 #include <nlohmann/detail/meta/std_fs.hpp>
 #include <nlohmann/detail/meta/type_traits.hpp>
+#include <nlohmann/detail/meta/logic.hpp>
 #include <nlohmann/detail/string_concat.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
@@ -446,13 +447,36 @@ inline void from_json(const BasicJsonType& j, ArithmeticType& val)
     }
 }
 
-template<typename BasicJsonType, typename... Args, std::size_t... Idx>
+template<typename BasicJsonType, typename Type>
-std::tuple<Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<Idx...> /*unused*/)
+detail::uncvref_t<Type> from_json_tuple_get_impl(BasicJsonType&& j, detail::identity_tag<Type> /*unused*/, detail::priority_tag<0> /*unused*/)
 {
-    return std::make_tuple(std::forward<BasicJsonType>(j).at(Idx).template get<Args>()...);
+    return std::forward<BasicJsonType>(j).template get<detail::uncvref_t<Type>>();
 }
 
-template<typename BasicJsonType>
+template<typename BasicJsonType, typename Type,
+         detail::enable_if_t<detail::is_compatible_reference_type<BasicJsonType, Type>::value, int> = 0>
+Type from_json_tuple_get_impl(BasicJsonType && j, detail::identity_tag<Type> /*unused*/, detail::priority_tag<1> /*unused*/)
+{
+    return std::forward<BasicJsonType>(j).template get_ref<Type>();
+}
+
+template<typename BasicJsonType, typename Type,
+         detail::enable_if_t<std::is_arithmetic<uncvref_t<Type>>::value, int> = 0>
+detail::uncvref_t<Type> from_json_tuple_get_impl(BasicJsonType && j, detail::identity_tag<Type> /*unused*/, detail::priority_tag<2> /*unused*/)
+{
+    return std::forward<BasicJsonType>(j).template get<detail::uncvref_t<Type>>();
+}
+
+template<std::size_t PTagValue, typename BasicJsonType, typename... Types>
+using tuple_type = std::tuple < decltype(from_json_tuple_get_impl(std::declval<BasicJsonType>(), detail::identity_tag<Types> {}, detail::priority_tag<PTagValue> {}))... >;
+
+template<std::size_t PTagValue, typename... Args, typename BasicJsonType, std::size_t... Idx>
+tuple_type<PTagValue, BasicJsonType, Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<Idx...> /*unused*/)
+{
+    return tuple_type<PTagValue, BasicJsonType, Args...>(from_json_tuple_get_impl(std::forward<BasicJsonType>(j).at(Idx), detail::identity_tag<Args> {}, detail::priority_tag<PTagValue> {})...);
+}
+
+template<std::size_t PTagValue, typename BasicJsonType>
 std::tuple<> from_json_tuple_impl_base(BasicJsonType& /*unused*/, index_sequence<> /*unused*/)
 {
     return {};
@@ -474,13 +498,15 @@ inline void from_json_tuple_impl(BasicJsonType&& j, std::pair<A1, A2>& p, priori
 template<typename BasicJsonType, typename... Args>
 std::tuple<Args...> from_json_tuple_impl(BasicJsonType&& j, identity_tag<std::tuple<Args...>> /*unused*/, priority_tag<2> /*unused*/)
 {
-    return from_json_tuple_impl_base<BasicJsonType, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
+    static_assert(cxpr_and<cxpr_or<cxpr_not<std::is_reference<Args>>, is_compatible_reference_type<BasicJsonType, Args>>...>::value,
+                  "Can not return a tuple containing references to types not contained in a Json, try Json::get_to()");
+    return from_json_tuple_impl_base<1, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
 }
 
 template<typename BasicJsonType, typename... Args>
 inline void from_json_tuple_impl(BasicJsonType&& j, std::tuple<Args...>& t, priority_tag<3> /*unused*/)
 {
-    t = from_json_tuple_impl_base<BasicJsonType, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
+    t = from_json_tuple_impl_base<2, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
 }
 
 template<typename BasicJsonType, typename TupleRelated>

include/nlohmann/detail/meta/logic.hpp

@@ -0,0 +1,54 @@
+#pragma once
+
+#include <nlohmann/detail/macro_scope.hpp>
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+#ifdef JSON_HAS_CPP_17
+
+template<bool... Booleans>
+struct cxpr_or_impl : std::integral_constant < bool, (Booleans || ...) > {};
+
+template<bool... Booleans>
+struct cxpr_and_impl : std::integral_constant < bool, (Booleans &&...) > {};
+
+#else
+
+template<bool... Booleans>
+struct cxpr_or_impl : std::false_type {};
+
+template<bool... Booleans>
+struct cxpr_or_impl<true, Booleans...> : std::true_type {};
+
+template<bool... Booleans>
+struct cxpr_or_impl<false, Booleans...> : cxpr_or_impl<Booleans...> {};
+
+template<bool... Booleans>
+struct cxpr_and_impl : std::true_type {};
+
+template<bool... Booleans>
+struct cxpr_and_impl<true, Booleans...> : cxpr_and_impl<Booleans...> {};
+
+template<bool... Booleans>
+struct cxpr_and_impl<false, Booleans...> : std::false_type {};
+
+#endif
+
+template<class Boolean>
+struct cxpr_not : std::integral_constant < bool, !Boolean::value > {};
+
+template<class... Booleans>
+struct cxpr_or : cxpr_or_impl<Booleans::value...> {};
+
+template<bool... Booleans>
+struct cxpr_or_c : cxpr_or_impl<Booleans...> {};
+
+template<class... Booleans>
+struct cxpr_and : cxpr_and_impl<Booleans::value...> {};
+
+template<bool... Booleans>
+struct cxpr_and_c : cxpr_and_impl<Booleans...> {};
+
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/meta/type_traits.hpp

@@ -559,6 +559,28 @@ template<typename BasicJsonType, typename CompatibleType>
 struct is_compatible_type
     : is_compatible_type_impl<BasicJsonType, CompatibleType> {};
 
+template<typename BasicJsonType, typename CompatibleReferenceType>
+struct is_compatible_reference_type_impl
+{
+    using JsonType = uncvref_t<BasicJsonType>;
+    using CVType = typename std::remove_reference<CompatibleReferenceType>::type;
+    using Type = typename std::remove_cv<CVType>::type;
+    constexpr static bool value = std::is_reference<CompatibleReferenceType>::value &&
+                                  (!std::is_const<typename std::remove_reference<BasicJsonType>::type>::value || std::is_const<CVType>::value) &&
+                                  (std::is_same<typename JsonType::boolean_t, Type>::value ||
+                                   std::is_same<typename JsonType::number_float_t, Type>::value ||
+                                   std::is_same<typename JsonType::number_integer_t, Type>::value ||
+                                   std::is_same<typename JsonType::number_unsigned_t, Type>::value ||
+                                   std::is_same<typename JsonType::string_t, Type>::value ||
+                                   std::is_same<typename JsonType::binary_t, Type>::value ||
+                                   std::is_same<typename JsonType::object_t, Type>::value ||
+                                   std::is_same<typename JsonType::array_t, Type>::value);
+};
+
+template<typename BasicJsonType, typename CompatibleReferenceType>
+struct is_compatible_reference_type
+    : is_compatible_reference_type_impl<BasicJsonType, CompatibleReferenceType> {};
+
 template<typename T1, typename T2>
 struct is_constructible_tuple : std::false_type {};
 

single_include/nlohmann/json.hpp

@@ -4103,6 +4103,28 @@ template<typename BasicJsonType, typename CompatibleType>
 struct is_compatible_type
     : is_compatible_type_impl<BasicJsonType, CompatibleType> {};
 
+template<typename BasicJsonType, typename CompatibleReferenceType>
+struct is_compatible_reference_type_impl
+{
+    using JsonType = uncvref_t<BasicJsonType>;
+    using CVType = typename std::remove_reference<CompatibleReferenceType>::type;
+    using Type = typename std::remove_cv<CVType>::type;
+    constexpr static bool value = std::is_reference<CompatibleReferenceType>::value &&
+                                  (!std::is_const<typename std::remove_reference<BasicJsonType>::type>::value || std::is_const<CVType>::value) &&
+                                  (std::is_same<typename JsonType::boolean_t, Type>::value ||
+                                   std::is_same<typename JsonType::number_float_t, Type>::value ||
+                                   std::is_same<typename JsonType::number_integer_t, Type>::value ||
+                                   std::is_same<typename JsonType::number_unsigned_t, Type>::value ||
+                                   std::is_same<typename JsonType::string_t, Type>::value ||
+                                   std::is_same<typename JsonType::binary_t, Type>::value ||
+                                   std::is_same<typename JsonType::object_t, Type>::value ||
+                                   std::is_same<typename JsonType::array_t, Type>::value);
+};
+
+template<typename BasicJsonType, typename CompatibleReferenceType>
+struct is_compatible_reference_type
+    : is_compatible_reference_type_impl<BasicJsonType, CompatibleReferenceType> {};
+
 template<typename T1, typename T2>
 struct is_constructible_tuple : std::false_type {};
 
@@ -4860,6 +4882,63 @@ NLOHMANN_JSON_NAMESPACE_END
 
 // #include <nlohmann/detail/meta/type_traits.hpp>
 
+// #include <nlohmann/detail/meta/logic.hpp>
+
+
+// #include <nlohmann/detail/macro_scope.hpp>
+
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+#ifdef JSON_HAS_CPP_17
+
+template<bool... Booleans>
+struct cxpr_or_impl : std::integral_constant < bool, (Booleans || ...) > {};
+
+template<bool... Booleans>
+struct cxpr_and_impl : std::integral_constant < bool, (Booleans &&...) > {};
+
+#else
+
+template<bool... Booleans>
+struct cxpr_or_impl : std::false_type {};
+
+template<bool... Booleans>
+struct cxpr_or_impl<true, Booleans...> : std::true_type {};
+
+template<bool... Booleans>
+struct cxpr_or_impl<false, Booleans...> : cxpr_or_impl<Booleans...> {};
+
+template<bool... Booleans>
+struct cxpr_and_impl : std::true_type {};
+
+template<bool... Booleans>
+struct cxpr_and_impl<true, Booleans...> : cxpr_and_impl<Booleans...> {};
+
+template<bool... Booleans>
+struct cxpr_and_impl<false, Booleans...> : std::false_type {};
+
+#endif
+
+template<class Boolean>
+struct cxpr_not : std::integral_constant < bool, !Boolean::value > {};
+
+template<class... Booleans>
+struct cxpr_or : cxpr_or_impl<Booleans::value...> {};
+
+template<bool... Booleans>
+struct cxpr_or_c : cxpr_or_impl<Booleans...> {};
+
+template<class... Booleans>
+struct cxpr_and : cxpr_and_impl<Booleans::value...> {};
+
+template<bool... Booleans>
+struct cxpr_and_c : cxpr_and_impl<Booleans...> {};
+
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END
+
 // #include <nlohmann/detail/string_concat.hpp>
 
 // #include <nlohmann/detail/value_t.hpp>
@@ -5282,13 +5361,36 @@ inline void from_json(const BasicJsonType& j, ArithmeticType& val)
     }
 }
 
-template<typename BasicJsonType, typename... Args, std::size_t... Idx>
+template<typename BasicJsonType, typename Type>
-std::tuple<Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<Idx...> /*unused*/)
+detail::uncvref_t<Type> from_json_tuple_get_impl(BasicJsonType&& j, detail::identity_tag<Type> /*unused*/, detail::priority_tag<0> /*unused*/)
 {
-    return std::make_tuple(std::forward<BasicJsonType>(j).at(Idx).template get<Args>()...);
+    return std::forward<BasicJsonType>(j).template get<detail::uncvref_t<Type>>();
 }
 
-template<typename BasicJsonType>
+template<typename BasicJsonType, typename Type,
+         detail::enable_if_t<detail::is_compatible_reference_type<BasicJsonType, Type>::value, int> = 0>
+Type from_json_tuple_get_impl(BasicJsonType && j, detail::identity_tag<Type> /*unused*/, detail::priority_tag<1> /*unused*/)
+{
+    return std::forward<BasicJsonType>(j).template get_ref<Type>();
+}
+
+template<typename BasicJsonType, typename Type,
+         detail::enable_if_t<std::is_arithmetic<uncvref_t<Type>>::value, int> = 0>
+detail::uncvref_t<Type> from_json_tuple_get_impl(BasicJsonType && j, detail::identity_tag<Type> /*unused*/, detail::priority_tag<2> /*unused*/)
+{
+    return std::forward<BasicJsonType>(j).template get<detail::uncvref_t<Type>>();
+}
+
+template<std::size_t PTagValue, typename BasicJsonType, typename... Types>
+using tuple_type = std::tuple < decltype(from_json_tuple_get_impl(std::declval<BasicJsonType>(), detail::identity_tag<Types> {}, detail::priority_tag<PTagValue> {}))... >;
+
+template<std::size_t PTagValue, typename... Args, typename BasicJsonType, std::size_t... Idx>
+tuple_type<PTagValue, BasicJsonType, Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<Idx...> /*unused*/)
+{
+    return tuple_type<PTagValue, BasicJsonType, Args...>(from_json_tuple_get_impl(std::forward<BasicJsonType>(j).at(Idx), detail::identity_tag<Args> {}, detail::priority_tag<PTagValue> {})...);
+}
+
+template<std::size_t PTagValue, typename BasicJsonType>
 std::tuple<> from_json_tuple_impl_base(BasicJsonType& /*unused*/, index_sequence<> /*unused*/)
 {
     return {};
@@ -5310,13 +5412,15 @@ inline void from_json_tuple_impl(BasicJsonType&& j, std::pair<A1, A2>& p, priori
 template<typename BasicJsonType, typename... Args>
 std::tuple<Args...> from_json_tuple_impl(BasicJsonType&& j, identity_tag<std::tuple<Args...>> /*unused*/, priority_tag<2> /*unused*/)
 {
-    return from_json_tuple_impl_base<BasicJsonType, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
+    static_assert(cxpr_and<cxpr_or<cxpr_not<std::is_reference<Args>>, is_compatible_reference_type<BasicJsonType, Args>>...>::value,
+                  "Can not return a tuple containing references to types not contained in a Json, try Json::get_to()");
+    return from_json_tuple_impl_base<1, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
 }
 
 template<typename BasicJsonType, typename... Args>
 inline void from_json_tuple_impl(BasicJsonType&& j, std::tuple<Args...>& t, priority_tag<3> /*unused*/)
 {
-    t = from_json_tuple_impl_base<BasicJsonType, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
+    t = from_json_tuple_impl_base<2, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
 }
 
 template<typename BasicJsonType, typename TupleRelated>

tests/src/unit-constructor1.cpp

@@ -281,6 +281,79 @@ TEST_CASE("constructors")
             // CHECK(std::get<2>(t) == j[2]); // commented out due to CI issue, see https://github.com/nlohmann/json/pull/3985 and https://github.com/nlohmann/json/issues/4025
         }
 
+        SECTION("std::tuple tie")
+        {
+            const auto a = 1.0;
+            const auto* const b = "string";
+            const auto c = 42;
+            const auto d = std::vector<int> {0, 2};
+            const size_t e = 1234;
+            auto t = std::tie(a, b, c, d, e);
+            json const j(t);
+
+            double a_out = 0;
+            std::string b_out;
+            int c_out = 0;
+            std::vector<int> d_out;
+            int64_t e_out = 0;
+            auto t_out = std::tie(a_out, b_out, c_out, d_out, e_out);
+            j.get_to(t_out);
+            CHECK(a_out == a);
+            CHECK(b_out == b);
+            CHECK(c_out == c);
+            CHECK(d_out == d);
+            CHECK(e_out == e);
+        }
+
+        SECTION("std::tuple of references to elements")
+        {
+            const auto a = 1.0;
+            const auto* const b = "string";
+            const auto c = 42;
+            const size_t d = 1234;
+            const auto t = std::tie(a, b, c, d);
+            json const j(t);
+
+            auto t_out = j.get<std::tuple<const json::number_float_t&,
+                 const json::string_t&,
+                 const json::number_integer_t&,
+                 const json::number_unsigned_t&>>();
+            CHECK(&std::get<0>(t_out) == j[0].get_ptr<const json::number_float_t*>());
+            CHECK(&std::get<1>(t_out) == j[1].get_ptr<const json::string_t*>());
+            CHECK(&std::get<2>(t_out) == j[2].get_ptr<const json::number_integer_t*>());
+            CHECK(&std::get<3>(t_out) == j[3].get_ptr<const json::number_unsigned_t*>());
+            CHECK(std::get<0>(t_out) == a);
+            CHECK(std::get<1>(t_out) == b);
+            CHECK(std::get<2>(t_out) == c);
+            CHECK(std::get<3>(t_out) == d);
+        }
+
+        SECTION("std::tuple mixed arithmetic types")
+        {
+            using j_float_t = json::number_float_t;
+            using j_int_t = json::number_integer_t;
+            using j_uint_t = json::number_unsigned_t;
+            const j_float_t a = 1.0;
+            const j_int_t b = 1234;
+            const j_uint_t c = 42;
+            json const j(std::tie(a, b, c, c));
+
+            auto t1 = j.get<std::tuple<j_int_t, j_uint_t, j_float_t, const j_uint_t&>>();
+            j_uint_t a2 = 0;
+            j_float_t b2 = 0;
+            j_int_t c2 = 0;
+            auto t2 = std::tie(a2, b2, c2);
+            j.get_to(t2);
+
+            CHECK(std::get<0>(t1) == static_cast<j_int_t>(a));
+            CHECK(std::get<1>(t1) == static_cast<j_uint_t>(b));
+            CHECK(std::get<2>(t1) == static_cast<j_float_t>(c));
+            // t1[3] exists only to force usage of the no-default-constructor version
+            CHECK(a2 == static_cast<j_uint_t>(a));
+            CHECK(b2 == static_cast<j_float_t>(b));
+            CHECK(c2 == static_cast<j_int_t>(c));
+        }
+
         SECTION("std::pair/tuple/array failures")
         {
             json const j{1};