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Use copy_cv_ref in apply_cv_ref instead of variant_alternative_t

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This commit is contained in:
Peter Dimov
2019-02-22 01:57:09 +02:00
parent c1287f9e95
commit a0b499bc3b
1 changed files with 35 additions and 20 deletions
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55
include/boost/variant2/variant.hpp
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@ -1585,6 +1585,40 @@ template<class... T> constexpr bool operator>=( variant<T...> const & v, variant
namespace detail
{
template<class T> using remove_cv_ref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
template<class T, class U> struct copy_cv_ref
{
using type = T;
};
template<class T, class U> struct copy_cv_ref<T, U const>
{
using type = T const;
};
template<class T, class U> struct copy_cv_ref<T, U volatile>
{
using type = T volatile;
};
template<class T, class U> struct copy_cv_ref<T, U const volatile>
{
using type = T const volatile;
};
template<class T, class U> struct copy_cv_ref<T, U&>
{
using type = typename copy_cv_ref<T, U>::type&;
};
template<class T, class U> struct copy_cv_ref<T, U&&>
{
using type = typename copy_cv_ref<T, U>::type&&;
};
template<class T, class U> using copy_cv_ref_t = typename copy_cv_ref<T, U>::type;
template<class F> struct Qret
{
template<class... T> using fn = decltype( std::declval<F>()( std::declval<T>()... ) );
@ -1592,26 +1626,7 @@ template<class F> struct Qret
template<class L> using front_if_same = mp11::mp_if<mp11::mp_apply<mp11::mp_same, L>, mp11::mp_front<L>>;
template<class N, class V> using var_alt = variant_alternative_t<N::value, V>;
#if BOOST_WORKAROUND( BOOST_MSVC, < 1920 )
template<class V> struct apply_cv_ref_impl
{
template<class N> using _f = var_alt<N, V>;
using L = mp11::mp_iota<variant_size<V>>;
using type = mp11::mp_transform<_f, L>;
};
template<class V> using apply_cv_ref = typename apply_cv_ref_impl<V>::type;
#else
template<class V> using apply_cv_ref = mp11::mp_transform_q<mp11::mp_bind_back<var_alt, V>, mp11::mp_iota<variant_size<V>>>;
#endif
template<class V> using apply_cv_ref = mp11::mp_product<copy_cv_ref_t, remove_cv_ref_t<V>, mp11::mp_list<V>>;
template<class F, class... V> using Vret = front_if_same<mp11::mp_product_q<Qret<F>, apply_cv_ref<V>...>>;