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use a priority_tag instead of int and longs with sfinae-dispatch

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This commit is contained in:
Théo DELRIEU 2017-01-14 02:33:03 +01:00
parent b8012876a5
commit 63e4249e9f
1 changed files with 16 additions and 12 deletions
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28
src/json.hpp
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@ -189,6 +189,11 @@ template <typename Json> std::string type_name(Json const &j)
}
}
// dispatch utility (taken from ranges-v3)
template <unsigned N> struct priority_tag : priority_tag<N - 1> {};
template <> struct priority_tag<0> {};
// This is an experiment. I need this to move constructors out of basic_json.
// I'm sure there is a better way, but this might need a big basic_json refactoring
template <value_t> struct external_constructor;
@ -642,9 +647,8 @@ void from_json(Json const&j, std::forward_list<T, Allocator>& l)
l.push_front(it->template get<T>());
}
template <typename Json, typename CompatibleArrayType>
void from_json_array_impl(Json const &j, CompatibleArrayType &arr, long)
void from_json_array_impl(Json const &j, CompatibleArrayType &arr, priority_tag<0>)
{
using std::begin;
using std::end;
@ -659,7 +663,7 @@ void from_json_array_impl(Json const &j, CompatibleArrayType &arr, long)
}
template <typename Json, typename CompatibleArrayType>
auto from_json_array_impl(Json const &j, CompatibleArrayType &arr, int)
auto from_json_array_impl(Json const &j, CompatibleArrayType &arr, priority_tag<1>)
-> decltype(
arr.reserve(std::declval<typename CompatibleArrayType::size_type>()),
void())
@ -693,7 +697,7 @@ void from_json(Json const &j, CompatibleArrayType &arr)
if (!j.is_array())
throw std::domain_error("type must be array, but is " + type_name(j));
}
from_json_array_impl(j, arr, 0);
from_json_array_impl(j, arr, priority_tag<1>{});
}
@ -744,7 +748,7 @@ void from_json(Json const &j, ArithmeticType &val)
struct to_json_fn
{
template <typename Json, typename T>
auto call(int, Json& j, T&& val) const
auto call(Json& j, T&& val, priority_tag<1>) const
noexcept(noexcept(to_json(j, std::forward<T>(val))))
-> decltype(to_json(j, std::forward<T>(val)),
void())
@ -753,7 +757,7 @@ struct to_json_fn
}
template <typename Json, typename T>
void call(long, Json&, T&&) const noexcept
void call(Json&, T&&, priority_tag<0>) const noexcept
{
static_assert(sizeof(Json) == 0, "to_json method in T's namespace can not be called");
}
@ -761,9 +765,9 @@ struct to_json_fn
public:
template <typename Json, typename T>
void operator()(Json &j, T &&val) const
noexcept(noexcept(std::declval<to_json_fn>().call(0, j, std::forward<T>(val))))
noexcept(noexcept(std::declval<to_json_fn>().call(j, std::forward<T>(val), priority_tag<1>{})))
{
return call(0, j, std::forward<T>(val));
return call(j, std::forward<T>(val), priority_tag<1>{});
}
};
@ -771,7 +775,7 @@ struct from_json_fn
{
private:
template <typename Json, typename T>
auto call(int, Json const &j, T &val) const
auto call(Json const &j, T &val, priority_tag<1>) const
noexcept(noexcept(from_json(j, val)))
-> decltype(from_json(j, val), void())
{
@ -779,7 +783,7 @@ private:
}
template <typename Json, typename T>
void call(long, Json const&, T&) const noexcept
void call(Json const&, T&, priority_tag<0>) const noexcept
{
static_assert(sizeof(Json) == 0, "from_json method in T's namespace can not be called");
}
@ -787,9 +791,9 @@ private:
public:
template <typename Json, typename T>
void operator()(Json const &j, T &val) const
noexcept(noexcept(std::declval<from_json_fn>().call(0, j, val)))
noexcept(noexcept(std::declval<from_json_fn>().call(j, val, priority_tag<1>{})))
{
return call(0, j, val);
return call(j, val, priority_tag<1>{});
}
};