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fix sfinae on basic_json UDT constructor #919

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merged 1 commit into from
Jan 23, 2018
Merged

fix sfinae on basic_json UDT constructor #919

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26 changes: 25 additions & 1 deletion develop/detail/meta.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -96,6 +96,14 @@ template<> struct priority_tag<0> {};
// has_/is_ functions //
////////////////////////

// source: https://stackoverflow.com/a/37193089/4116453

template <typename T, typename = void>
struct is_complete_type : std::false_type {};

template <typename T>
struct is_complete_type<T, decltype(void(sizeof(T)))> : std::true_type {};

NLOHMANN_JSON_HAS_HELPER(mapped_type);
NLOHMANN_JSON_HAS_HELPER(key_type);
NLOHMANN_JSON_HAS_HELPER(value_type);
Expand Down Expand Up @@ -171,7 +179,6 @@ struct is_compatible_integer_type
RealIntegerType, CompatibleNumberIntegerType > ::value;
};


// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
template<typename BasicJsonType, typename T>
struct has_from_json
Expand Down Expand Up @@ -221,6 +228,23 @@ struct has_to_json
std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
};

template <typename BasicJsonType, typename CompatibleCompleteType>
struct is_compatible_complete_type
{
static constexpr bool value =
not std::is_base_of<std::istream, CompatibleCompleteType>::value and
not std::is_same<BasicJsonType, CompatibleCompleteType>::value and
not is_basic_json_nested_type<BasicJsonType, CompatibleCompleteType>::value and
has_to_json<BasicJsonType, CompatibleCompleteType>::value;
};

template <typename BasicJsonType, typename CompatibleType>
struct is_compatible_type
: conjunction<is_complete_type<CompatibleType>,
is_compatible_complete_type<BasicJsonType, CompatibleType>>
{
};

// taken from ranges-v3
template<typename T>
struct static_const
Expand Down
16 changes: 7 additions & 9 deletions develop/json.hpp
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Expand Up @@ -1551,15 +1551,13 @@ class basic_json

@since version 2.1.0
*/
template<typename CompatibleType, typename U = detail::uncvref_t<CompatibleType>,
detail::enable_if_t<not std::is_base_of<std::istream, U>::value and
not std::is_same<U, basic_json_t>::value and
not detail::is_basic_json_nested_type<
basic_json_t, U>::value and
detail::has_to_json<basic_json, U>::value,
int> = 0>
basic_json(CompatibleType && val) noexcept(noexcept(JSONSerializer<U>::to_json(
std::declval<basic_json_t&>(), std::forward<CompatibleType>(val))))
template <typename CompatibleType,
typename U = detail::uncvref_t<CompatibleType>,
detail::enable_if_t<
detail::is_compatible_type<basic_json_t, U>::value, int> = 0>
basic_json(CompatibleType && val) noexcept(noexcept(
JSONSerializer<U>::to_json(std::declval<basic_json_t&>(),
std::forward<CompatibleType>(val))))
{
JSONSerializer<U>::to_json(*this, std::forward<CompatibleType>(val));
assert_invariant();
Expand Down
42 changes: 32 additions & 10 deletions src/json.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -312,6 +312,14 @@ template<> struct priority_tag<0> {};
// has_/is_ functions //
////////////////////////

// source: https://stackoverflow.com/a/37193089/4116453

template <typename T, typename = void>
struct is_complete_type : std::false_type {};

template <typename T>
struct is_complete_type<T, decltype(void(sizeof(T)))> : std::true_type {};

NLOHMANN_JSON_HAS_HELPER(mapped_type);
NLOHMANN_JSON_HAS_HELPER(key_type);
NLOHMANN_JSON_HAS_HELPER(value_type);
Expand Down Expand Up @@ -387,7 +395,6 @@ struct is_compatible_integer_type
RealIntegerType, CompatibleNumberIntegerType > ::value;
};


// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
template<typename BasicJsonType, typename T>
struct has_from_json
Expand Down Expand Up @@ -437,6 +444,23 @@ struct has_to_json
std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
};

template <typename BasicJsonType, typename CompatibleCompleteType>
struct is_compatible_complete_type
{
static constexpr bool value =
not std::is_base_of<std::istream, CompatibleCompleteType>::value and
not std::is_same<BasicJsonType, CompatibleCompleteType>::value and
not is_basic_json_nested_type<BasicJsonType, CompatibleCompleteType>::value and
has_to_json<BasicJsonType, CompatibleCompleteType>::value;
};

template <typename BasicJsonType, typename CompatibleType>
struct is_compatible_type
: conjunction<is_complete_type<CompatibleType>,
is_compatible_complete_type<BasicJsonType, CompatibleType>>
{
};

// taken from ranges-v3
template<typename T>
struct static_const
Expand Down Expand Up @@ -8839,15 +8863,13 @@ class basic_json

@since version 2.1.0
*/
template<typename CompatibleType, typename U = detail::uncvref_t<CompatibleType>,
detail::enable_if_t<not std::is_base_of<std::istream, U>::value and
not std::is_same<U, basic_json_t>::value and
not detail::is_basic_json_nested_type<
basic_json_t, U>::value and
detail::has_to_json<basic_json, U>::value,
int> = 0>
basic_json(CompatibleType && val) noexcept(noexcept(JSONSerializer<U>::to_json(
std::declval<basic_json_t&>(), std::forward<CompatibleType>(val))))
template <typename CompatibleType,
typename U = detail::uncvref_t<CompatibleType>,
detail::enable_if_t<
detail::is_compatible_type<basic_json_t, U>::value, int> = 0>
basic_json(CompatibleType && val) noexcept(noexcept(
JSONSerializer<U>::to_json(std::declval<basic_json_t&>(),
std::forward<CompatibleType>(val))))
{
JSONSerializer<U>::to_json(*this, std::forward<CompatibleType>(val));
assert_invariant();
Expand Down
19 changes: 19 additions & 0 deletions test/src/unit-udt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -692,3 +692,22 @@ TEST_CASE("custom serializer that does adl by default", "[udt]")
CHECK(me == j.get<udt::person>());
CHECK(me == cj.get<udt::person>());
}

namespace
{
struct incomplete;

// std::is_constructible is broken on macOS' libc++
// use the cppreference implementation

template <typename T, typename = void>
struct is_constructible_patched : std::false_type {};

template <typename T>
struct is_constructible_patched<T, decltype(void(json(std::declval<T>())))> : std::true_type {};
}

TEST_CASE("an incomplete type does not trigger a compiler error in non-evaluated context", "[udt]")
{
static_assert(not is_constructible_patched<json, incomplete>::value, "");
}