Merge pull request #919 from theodelrieu/fix/sfinae_for_incomplete_types
fix sfinae on basic_json UDT constructor
This commit is contained in:
Niels Lohmann
GitHub
commit
f5c4e9f3a1
4 changed files with 83 additions and 20 deletions
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@ -96,6 +96,14 @@ template<> struct priority_tag<0> {};
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// has_/is_ functions //
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////////////////////////
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// source: https://stackoverflow.com/a/37193089/4116453
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template <typename T, typename = void>
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struct is_complete_type : std::false_type {};
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template <typename T>
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struct is_complete_type<T, decltype(void(sizeof(T)))> : std::true_type {};
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NLOHMANN_JSON_HAS_HELPER(mapped_type);
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NLOHMANN_JSON_HAS_HELPER(key_type);
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NLOHMANN_JSON_HAS_HELPER(value_type);
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@ -171,7 +179,6 @@ struct is_compatible_integer_type
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RealIntegerType, CompatibleNumberIntegerType > ::value;
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};
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// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
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template<typename BasicJsonType, typename T>
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struct has_from_json
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@ -221,6 +228,23 @@ struct has_to_json
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std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
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};
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template <typename BasicJsonType, typename CompatibleCompleteType>
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struct is_compatible_complete_type
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{
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static constexpr bool value =
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not std::is_base_of<std::istream, CompatibleCompleteType>::value and
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not std::is_same<BasicJsonType, CompatibleCompleteType>::value and
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not is_basic_json_nested_type<BasicJsonType, CompatibleCompleteType>::value and
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has_to_json<BasicJsonType, CompatibleCompleteType>::value;
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};
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template <typename BasicJsonType, typename CompatibleType>
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struct is_compatible_type
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: conjunction<is_complete_type<CompatibleType>,
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is_compatible_complete_type<BasicJsonType, CompatibleType>>
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{
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};
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// taken from ranges-v3
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template<typename T>
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struct static_const
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@ -1551,15 +1551,13 @@ class basic_json
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@since version 2.1.0
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*/
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template<typename CompatibleType, typename U = detail::uncvref_t<CompatibleType>,
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detail::enable_if_t<not std::is_base_of<std::istream, U>::value and
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not std::is_same<U, basic_json_t>::value and
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not detail::is_basic_json_nested_type<
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basic_json_t, U>::value and
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detail::has_to_json<basic_json, U>::value,
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int> = 0>
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basic_json(CompatibleType && val) noexcept(noexcept(JSONSerializer<U>::to_json(
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std::declval<basic_json_t&>(), std::forward<CompatibleType>(val))))
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template <typename CompatibleType,
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typename U = detail::uncvref_t<CompatibleType>,
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detail::enable_if_t<
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detail::is_compatible_type<basic_json_t, U>::value, int> = 0>
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basic_json(CompatibleType && val) noexcept(noexcept(
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JSONSerializer<U>::to_json(std::declval<basic_json_t&>(),
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std::forward<CompatibleType>(val))))
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{
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JSONSerializer<U>::to_json(*this, std::forward<CompatibleType>(val));
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assert_invariant();
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42
src/json.hpp
42
src/json.hpp
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@ -310,6 +310,14 @@ template<> struct priority_tag<0> {};
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// has_/is_ functions //
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////////////////////////
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// source: https://stackoverflow.com/a/37193089/4116453
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template <typename T, typename = void>
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struct is_complete_type : std::false_type {};
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template <typename T>
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struct is_complete_type<T, decltype(void(sizeof(T)))> : std::true_type {};
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NLOHMANN_JSON_HAS_HELPER(mapped_type);
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NLOHMANN_JSON_HAS_HELPER(key_type);
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NLOHMANN_JSON_HAS_HELPER(value_type);
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@ -385,7 +393,6 @@ struct is_compatible_integer_type
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RealIntegerType, CompatibleNumberIntegerType > ::value;
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};
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// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
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template<typename BasicJsonType, typename T>
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struct has_from_json
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@ -435,6 +442,23 @@ struct has_to_json
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std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
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};
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template <typename BasicJsonType, typename CompatibleCompleteType>
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struct is_compatible_complete_type
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{
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static constexpr bool value =
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not std::is_base_of<std::istream, CompatibleCompleteType>::value and
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not std::is_same<BasicJsonType, CompatibleCompleteType>::value and
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not is_basic_json_nested_type<BasicJsonType, CompatibleCompleteType>::value and
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has_to_json<BasicJsonType, CompatibleCompleteType>::value;
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};
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template <typename BasicJsonType, typename CompatibleType>
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struct is_compatible_type
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: conjunction<is_complete_type<CompatibleType>,
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is_compatible_complete_type<BasicJsonType, CompatibleType>>
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{
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};
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// taken from ranges-v3
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template<typename T>
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struct static_const
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@ -10379,15 +10403,13 @@ class basic_json
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@since version 2.1.0
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*/
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template<typename CompatibleType, typename U = detail::uncvref_t<CompatibleType>,
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detail::enable_if_t<not std::is_base_of<std::istream, U>::value and
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not std::is_same<U, basic_json_t>::value and
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not detail::is_basic_json_nested_type<
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basic_json_t, U>::value and
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detail::has_to_json<basic_json, U>::value,
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int> = 0>
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basic_json(CompatibleType && val) noexcept(noexcept(JSONSerializer<U>::to_json(
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std::declval<basic_json_t&>(), std::forward<CompatibleType>(val))))
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template <typename CompatibleType,
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typename U = detail::uncvref_t<CompatibleType>,
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detail::enable_if_t<
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detail::is_compatible_type<basic_json_t, U>::value, int> = 0>
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basic_json(CompatibleType && val) noexcept(noexcept(
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JSONSerializer<U>::to_json(std::declval<basic_json_t&>(),
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std::forward<CompatibleType>(val))))
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{
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JSONSerializer<U>::to_json(*this, std::forward<CompatibleType>(val));
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assert_invariant();
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@ -692,3 +692,22 @@ TEST_CASE("custom serializer that does adl by default", "[udt]")
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CHECK(me == j.get<udt::person>());
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CHECK(me == cj.get<udt::person>());
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}
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namespace
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{
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struct incomplete;
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// std::is_constructible is broken on macOS' libc++
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// use the cppreference implementation
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template <typename T, typename = void>
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struct is_constructible_patched : std::false_type {};
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template <typename T>
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struct is_constructible_patched<T, decltype(void(json(std::declval<T>())))> : std::true_type {};
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}
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TEST_CASE("an incomplete type does not trigger a compiler error in non-evaluated context", "[udt]")
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{
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static_assert(not is_constructible_patched<json, incomplete>::value, "");
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}
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