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add alias templates to reduce boilerplate

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This commit is contained in:
Théo DELRIEU 2016-10-18 23:45:58 +02:00
parent 733e95f4ae
commit 06d60de3aa
1 changed files with 33 additions and 27 deletions
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60
src/json.hpp
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@ -102,6 +102,17 @@ namespace nlohmann
template <typename T, typename = void>
struct json_traits;
// alias templates to reduce boilerplate
template <bool B, typename T = void>
using enable_if_t = typename std::enable_if<B, T>::type;
template <typename T>
using remove_cv_t = typename std::remove_cv<T>::type;
template <typename T>
using remove_reference_t = typename std::remove_reference<T>::type;
// TODO update this doc
/*!
@brief unnamed namespace with internal helper functions
@since version 1.0.0
@ -1304,15 +1315,11 @@ class basic_json
// auto j = json{{"a", json(not_equality_comparable{})}};
//
// we can remove this constraint though, since lots of ctor are not explicit already
template <
typename T,
typename =
typename std::enable_if<detail::has_json_traits<typename std::remove_cv<
typename std::remove_reference<T>::type>::type>::value>::type>
template <typename T, typename = enable_if_t<detail::has_json_traits<
remove_cv_t<remove_reference_t<T>>>::value>>
explicit basic_json(T &&val)
: basic_json(json_traits<typename std::remove_cv<
typename std::remove_reference<T>::type>::type>::
to_json(std::forward<T>(val))) {}
: basic_json(json_traits<remove_cv_t<remove_reference_t<T>>>::to_json(
std::forward<T>(val))) {}
/*!
@brief create a string (explicit)
@ -2673,17 +2680,12 @@ class basic_json
// get_impl overload chosen if json_traits struct is specialized for type T
// simply returns json_traits<T>::from_json(*this);
// TODO add alias templates (enable_if_t etc)
template <
typename T,
typename = typename std::enable_if<
detail::has_json_traits<typename std::remove_cv<
typename std::remove_reference<T>::type>::type>::value>::type>
auto get_impl(T *) const -> decltype(
json_traits<typename std::remove_cv<typename std::remove_reference<
T>::type>::type>::from_json(std::declval<basic_json>())) {
return json_traits<typename std::remove_cv<
typename std::remove_reference<T>::type>::type>::from_json(*this);
template <typename T, typename = enable_if_t<detail::has_json_traits<
remove_cv_t<remove_reference_t<T>>>::value>>
auto get_impl(T *) const
-> decltype(json_traits<remove_cv_t<remove_reference_t<T>>>::from_json(
std::declval<basic_json>())) {
return json_traits<remove_cv_t<remove_reference_t<T>>>::from_json(*this);
}
// this one is quite atrocious
@ -2691,15 +2693,19 @@ class basic_json
// I chose to prefer the json_traits specialization if it exists, since it's a more advanced use.
// But we can of course change this behaviour
template <typename T>
auto get_impl(T *) const -> typename std::enable_if<
not detail::has_json_traits<typename std::remove_cv<T>::type>::value,
typename std::remove_cv<typename std::remove_reference<
decltype(::nlohmann::from_json(std::declval<basic_json>(),
std::declval<T &>()),
std::declval<T>())>::type>::type>::type
auto get_impl(T *) const
-> enable_if_t<not detail::has_json_traits<remove_cv_t<T>>::value,
remove_cv_t<remove_reference_t<decltype(
::nlohmann::from_json(std::declval<basic_json>(),
std::declval<T &>()),
std::declval<T>())>>>
{
typename std::remove_cv<typename std::remove_reference<T>::type>::type
ret;
remove_cv_t<T> ret;
// I guess this output parameter is the only way to get ADL
// Even if users can use the get<T> method to have a more 'functional' behaviour
// i.e. having a return type, could there be a way to have the same behaviour with from_json?
// e.g. auto t = nlohmann::from_json<T>(json{});
// this seems to require variable templates though... (at least it did when I tried to implement it)
::nlohmann::from_json(*this, ret);
return ret;
}