Proposed resolution:
This wording is relative to N4885.
Modify [expos.only.func] as indicated:
-2- The following are defined for exposition only to aid in the specification of the library:
namespace std { template<class T> constexpr decay_t<T> decay-copy(T&& v) noexcept(is_nothrow_convertible_v<T, decay_t<T>>) // exposition only { return std::forward<T>(v); } constexpr auto synth-three-way = []<class T, class U>(const T& t, const U& u) requires requires { { t < u } -> boolean-testable; { u < t } -> boolean-testable; } { if constexpr (three_way_comparable_with<T, U>) { return t <=> u; } else { if (t < u) return weak_ordering::less; if (u < t) return weak_ordering::greater; return weak_ordering::equivalent; } }; template<class T, class U=T> using synth-three-way-result = decltype(synth-three-way(declval<T&>(), declval<U&>())); }
Modify [contents] as indicated:
-3-
Whenever a name x defined in the standard library is mentioned, the name x is assumed to be fully qualified as ::std::x, unless explicitly described otherwise. For example, if the Effects: element for library function F is described as calling library function G, the function ::std::G is meant.Whenever an unqualified name x is used in the specification of a declaration D in clauses 16-32 or Annex D, its meaning is established as-if by performing unqualified name lookup ([basic.lookup.unqual]) in the context of D. [Note ?: Argument-dependent lookup is not performed. — end note] Similarly, the meaning of a qualified-id is established as-if by performing qualified name lookup ([basic.lookup.qual]) in the context of D. [Example: The reference to is_array_v in the specification of std::to_array ([array.creation]) refers to ::std::is_array_v. — end example] [Note ?: Operators in expressions ([over.match.oper]) are not so constrained; see [global.functions]. — end note]
Modify [range.subrange.general] as indicated:
template<class T> concept pair-like = // exposition only !is_reference_v<T> && requires(T t) { typename tuple_size<T>::type; // ensures tuple_size<T> is complete requires derived_from<tuple_size<T>, integral_constant<size_t, 2>>; typename tuple_element_t<0, remove_const_t<T>>; typename tuple_element_t<1, remove_const_t<T>>; { std::get<0>(t) } -> convertible_to<const tuple_element_t<0, T>&>; { std::get<1>(t) } -> convertible_to<const tuple_element_t<1, T>&>; };
Modify [range.elements.view] as indicated:
template<class T, size_t N> concept has-tuple-element = // exposition only requires(T t) { typename tuple_size<T>::type; requires N <tuple_size_v<T>; typename tuple_element_t<N, T>; { std::get<N>(t) } -> convertible_to<const tuple_element_t<N, T>&>; };
Modify [range.elements.iterator] as indicated:
-2- The member typedef-name iterator_category is defined if and only if Base models forward_range. In that case, iterator_category is defined as follows: […]
(2.1) — If std::get<N>(*current_) is an rvalue, iterator_category denotes input_iterator_tag.
[…]
static constexpr decltype(auto) get-element(const iterator_t<Base>& i); // exposition only-3- Effects: Equivalent to:
if constexpr (is_reference_v<range_reference_t<Base>>) { return std::get<N>(*i); } else { using E = remove_cv_t<tuple_element_t<N, range_reference_t<Base>>>; return static_cast<E>(std::get<N>(*i)); }
Remove [fs.req.namespace] in its entirety:
29.11.3.2 Namespaces and headers [fs.req.namespace]
-1- Unless otherwise specified, references to entities described in subclause [filesystems] are assumed to be qualified with ::std::filesystem::.