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refactor is_compatible_type, remove conjunction & co

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Théo DELRIEU
2018-09-05 17:01:52 +02:00
parent 77967e6548
commit 29f72966c3
3 changed files with 24 additions and 60 deletions
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20
include/nlohmann/detail/meta/cpp_future.hpp
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@@ -46,26 +46,6 @@ template<> struct make_index_sequence<1> : index_sequence<0> {};
template<typename... Ts>
using index_sequence_for = make_index_sequence<sizeof...(Ts)>;
/*
Implementation of two C++17 constructs: conjunction, negation. This is needed
to avoid evaluating all the traits in a condition
For example: not std::is_same<void, T>::value and has_value_type<T>::value
will not compile when T = void (on MSVC at least). Whereas
conjunction<negation<std::is_same<void, T>>, has_value_type<T>>::value will
stop evaluating if negation<...>::value == false
Please note that those constructs must be used with caution, since symbols can
become very long quickly (which can slow down compilation and cause MSVC
internal compiler errors). Only use it when you have to (see example ahead).
*/
template<class...> struct conjunction : std::true_type {};
template<class B1> struct conjunction<B1> : B1 {};
template<class B1, class... Bn>
struct conjunction<B1, Bn...> : std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type {};
template<class B> struct negation : std::integral_constant<bool, not B::value> {};
// dispatch utility (taken from ranges-v3)
template<unsigned N> struct priority_tag : priority_tag < N - 1 > {};
template<> struct priority_tag<0> {};