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LWG Poll 1: P2315R0 LWG Tentatively Ready issues #4523

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Merged
merged 8 commits into from
Mar 8, 2021
Merged

LWG Poll 1: P2315R0 LWG Tentatively Ready issues #4523

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c2dc9b0
LWG3391 Problems with counted_iterator/move_iterator::base() const &
burblebee Feb 25, 2021
8be9a47
LWG3433 subrange::advance(n) has UB when n < 0
burblebee Feb 25, 2021
575978f
LWG3490 ranges::drop_while_view::begin() is missing a precondition
burblebee Feb 25, 2021
8e9f752
LWG3492 Minimal improvements to elements_view::iterator
burblebee Feb 25, 2021
dcddfb0
LWG3495 constexpr launder makes pointers to inactive members of union…
burblebee Feb 25, 2021
6deea4d
LWG3500 join_view::iterator::operator->() is bogus
burblebee Feb 25, 2021
21de0b0
LWG3502 elements_view should not be allowed to return dangling refere…
burblebee Feb 25, 2021
a0c8e90
LWG3505 split_view::outer-iterator::operator++ misspecified
burblebee Feb 25, 2021
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16 changes: 4 additions & 12 deletions source/iterators.tex
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4096,7 +4096,7 @@
template<class U> constexpr move_iterator(const move_iterator<U>& u);
template<class U> constexpr move_iterator& operator=(const move_iterator<U>& u);

constexpr iterator_type base() const &;
constexpr const iterator_type& base() const &;
constexpr iterator_type base() &&;
constexpr reference operator*() const;

Expand Down Expand Up @@ -4226,18 +4226,10 @@

\indexlibrarymember{base}{move_iterator}%
\begin{itemdecl}
constexpr Iterator base() const &;
constexpr const Iterator& base() const &;
\end{itemdecl}

\begin{itemdescr}
\pnum
\constraints
\tcode{Iterator} satisfies \libconcept{copy_constructible}.

\pnum
\expects
\tcode{Iterator} models \libconcept{copy_constructible}.

\pnum
\returns
\tcode{current}.
Expand Down Expand Up @@ -5170,7 +5162,7 @@
requires @\libconcept{assignable_from}@<I&, const I2&>
constexpr counted_iterator& operator=(const counted_iterator<I2>& x);

constexpr I base() const & requires copy_constructible<I>;
constexpr const I& base() const &;
constexpr I base() &&;
constexpr iter_difference_t<I> count() const noexcept;
constexpr decltype(auto) operator*();
Expand Down Expand Up @@ -5297,7 +5289,7 @@

\indexlibrarymember{base}{counted_iterator}%
\begin{itemdecl}
constexpr I base() const & requires copy_constructible<I>;
constexpr const I& base() const &;
\end{itemdecl}

\begin{itemdescr}
Expand Down
116 changes: 76 additions & 40 deletions source/ranges.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -1765,22 +1765,21 @@
\pnum
\effects
Equivalent to:
\begin{itemize}
\item If \exposid{StoreSize} is \tcode{true},
\begin{codeblock}
if constexpr (bidirectional_iterator<I>) {
if (n < 0) {
ranges::advance(@\exposid{begin_}@, n);
if constexpr (@\exposid{StoreSize}@)
@\exposid{size_}@ += @\placeholdernc{to-unsigned-like}@(-n);
return *this;
}
}

auto d = n - ranges::advance(@\exposid{begin_}@, n, @\exposid{end_}@);
if (d >= 0)
if constexpr (@\exposid{StoreSize}@)
@\exposid{size_}@ -= @\placeholdernc{to-unsigned-like}@(d);
else
@\exposid{size_}@ += @\placeholdernc{to-unsigned-like}@(-d);
return *this;
\end{codeblock}
\item Otherwise,
\begin{codeblock}
ranges::advance(@\exposid{begin_}@, n, @\exposid{end_}@);
return *this;
\end{codeblock}
\end{itemize}
\end{itemdescr}

\indexlibrarymember{get}{subrange}%
Expand Down Expand Up @@ -4914,6 +4913,10 @@
\end{itemdecl}

\begin{itemdescr}
\pnum
\expects
\tcode{\exposid{pred_}.has_value()} is \tcode{true}.

\pnum
\returns
\tcode{ranges::find_if_not(\exposid{base_}, cref(*\exposid{pred_}))}.
Expand Down Expand Up @@ -5053,16 +5056,17 @@
template<bool Const>
struct join_view<V>::@\exposid{iterator}@ {
private:
using @\exposid{Parent}@ = @\exposid{maybe-const}@<Const, join_view>; // \expos
using @\exposid{Base}@ = @\exposid{maybe-const}@<Const, V>; // \expos
using @\exposid{Parent}@ = @\exposid{maybe-const}@<Const, join_view>; // \expos
using @\exposid{Base}@ = @\exposid{maybe-const}@<Const, V>; // \expos
using @\exposid{OuterIter}@ = iterator_t<@\exposid{Base}@>; // \expos
using @\exposid{InnerIter}@ = iterator_t<range_reference_t<@\exposid{Base}@>>; // \expos

static constexpr bool @\exposid{ref-is-glvalue}@ = // \expos
is_reference_v<range_reference_t<@\exposid{Base}@>>;

iterator_t<@\exposid{Base}@> @\exposid{outer_}@ = iterator_t<@\exposid{Base}@>(); // \expos
iterator_t<range_reference_t<@\exposid{Base}@>> @\exposid{inner_}@ = // \expos
iterator_t<range_reference_t<@\exposid{Base}@>>();
@\exposid{Parent}@* @\exposid{parent_}@ = nullptr; // \expos
@\exposid{OuterIter}@ @\exposid{outer_}@ = @\exposid{OuterIter}@(); // \expos
@\exposid{InnerIter}@ @\exposid{inner_}@ = @\exposid{InnerIter}@(); // \expos
@\exposid{Parent}@* @\exposidnc{parent_}@ = nullptr; // \expos

constexpr void @\exposid{satisfy}@(); // \expos
public:
Expand All @@ -5072,17 +5076,16 @@
using difference_type = @\seebelow@;

@\exposid{iterator}@() = default;
constexpr @\exposid{iterator}@(@\exposid{Parent}@& parent, iterator_t<@\exposid{Base}@> outer);
constexpr @\exposid{iterator}@(@\exposid{Parent}@& parent, @\exposid{OuterIter}@ outer);
constexpr @\exposid{iterator}@(@\exposid{iterator}@<!Const> i)
requires Const &&
@\libconcept{convertible_to}@<iterator_t<V>, iterator_t<@\exposid{Base}@>> &&
@\libconcept{convertible_to}@<iterator_t<@\exposid{InnerRng}@>,
iterator_t<range_reference_t<@\exposid{Base}@>>>;
@\libconcept{convertible_to}@<iterator_t<V>, @\exposid{OuterIter}@> &&
@\libconcept{convertible_to}@<iterator_t<@\exposid{InnerRng}@>, @\exposid{InnerIter}@>;

constexpr decltype(auto) operator*() const { return *@\exposid{inner_}@; }

constexpr iterator_t<@\exposid{Base}@> operator->() const
requires @\exposconcept{has-arrow}@<iterator_t<@\exposid{Base}@>> && @\libconcept{copyable}@<iterator_t<@\exposid{Base}@>>;
constexpr @\exposid{InnerIter}@ operator->() const
requires @\exposconcept{has-arrow}@<@\exposid{InnerIter}@> && @\libconcept{copyable}@<@\exposid{InnerIter}@>;

constexpr @\exposid{iterator}@& operator++();
constexpr void operator++(int);
Expand Down Expand Up @@ -5185,13 +5188,13 @@
return;
}
if constexpr (@\exposid{ref-is-glvalue}@)
@\exposid{inner_}@ = iterator_t<range_reference_t<@\exposid{Base}@>>();
@\exposid{inner_}@ = @\exposid{InnerIter}@();
\end{codeblock}
\end{itemdescr}

\indexlibraryctor{join_view::iterator}%
\begin{itemdecl}
constexpr @\exposid{iterator}@(@\exposid{Parent}@& parent, iterator_t<@\exposid{Base}@> outer);
constexpr @\exposid{iterator}@(@\exposid{Parent}@& parent, @\exposid{OuterIter}@ outer);
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -5205,9 +5208,8 @@
\begin{itemdecl}
constexpr @\exposid{iterator}@(@\exposid{iterator}@<!Const> i)
requires Const &&
@\libconcept{convertible_to}@<iterator_t<V>, iterator_t<@\exposid{Base}@>> &&
@\libconcept{convertible_to}@<iterator_t<@\exposid{InnerRng}@>,
iterator_t<range_reference_t<@\exposid{Base}@>>>;
@\libconcept{convertible_to}@<iterator_t<V>, @\exposid{OuterIter}@> &&
@\libconcept{convertible_to}@<iterator_t<@\exposid{InnerRng}@>, @\exposid{InnerIter}@>;
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -5220,8 +5222,8 @@

\indexlibrarymember{operator->}{join_view::iterator}%
\begin{itemdecl}
constexpr iterator_t<@\exposid{Base}@> operator->() const
requires @\exposconcept{has-arrow}@<iterator_t<@\exposid{Base}@>> && copyable<iterator_t<@\exposid{Base}@>>;
constexpr @\exposid{InnerIter}@ operator->() const
requires @\exposconcept{has-arrow}@<@\exposid{InnerIter}@> && @\libconcept{copyable}@<@\exposid{InnerIter}@>;
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -5672,11 +5674,17 @@
if (@\placeholder{current}@ == end) return *this;
const auto [pbegin, pend] = subrange{@\exposid{parent_}@->@\exposid{pattern_}@};
if (pbegin == pend) ++@\placeholder{current}@;
else if constexpr (@\exposconcept{tiny-range}@<Pattern>) {
@\placeholder{current}@ = ranges::find(std::move(@\placeholder{current}@), end, *pbegin);
if (@\placeholder{current}@ != end) {
++@\placeholder{current}@;
}
}
else {
do {
auto [b, p] = ranges::mismatch(std::move(@\placeholder{current}@), end, pbegin, pend);
@\placeholder{current}@ = std::move(b);
auto [b, p] = ranges::mismatch(@\placeholder{current}@, end, pbegin, pend);
if (p == pend) {
@\placeholder{current}@ = b;
break; // The pattern matched; skip it
}
} while (++@\placeholder{current}@ != end);
Expand Down Expand Up @@ -6308,10 +6316,14 @@
{ get<N>(t) } -> convertible_to<const tuple_element_t<N, T>&>;
};

template<class T, size_t N>
concept @\defexposconcept{returnable-element}@ = // \expos
is_reference_v<T> || move_constructible<tuple_element_t<N, T>>;

template<@\libconcept{input_range}@ V, size_t N>
requires @\libconcept{view}@<V> && @\exposconcept{has-tuple-element}@<range_value_t<V>, N> &&
@\exposconcept{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N>
@\exposconcept{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N> &&
@\exposconcept{returnable-element}@<range_reference_t<V>, N>
class elements_view : public view_interface<elements_view<V, N>> {
public:
elements_view() = default;
Expand Down Expand Up @@ -6372,12 +6384,16 @@
namespace std::ranges {
template<@\libconcept{input_range}@ V, size_t N>
requires @\libconcept{view}@<V> && @\exposconcept{has-tuple-element}@<range_value_t<V>, N> &&
@\exposconcept{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N>
@\exposconcept{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N> &&
@\exposconcept{returnable-element}@<range_reference_t<V>, N>
template<bool Const>
class elements_view<V, N>::@\exposid{iterator}@ { // \expos
using @\exposid{Base}@ = @\exposid{maybe-const}@<Const, V>; // \expos

iterator_t<@\exposid{Base}@> @\exposid{current_}@ = iterator_t<@\exposid{Base}@>();
iterator_t<@\exposid{Base}@> @\exposid{current_}@ = iterator_t<@\exposid{Base}@>(); // \expos
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4e22857 should've been a "fixup:" commit, I think.

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oops, yes, it should have been. @tkoeppe can extract it when he merges if he cares enough (we used to be a lot more lax about fly-by fixes like this)


static constexpr decltype(auto) @\exposid{get-element}@(const iterator_t<@\exposid{Base}@>& i); // \expos

public:
using iterator_category = typename iterator_traits<iterator_t<@\exposid{Base}@>>::iterator_category;
using value_type = remove_cvref_t<tuple_element_t<N, range_value_t<@\exposid{Base}@>>>;
Expand All @@ -6393,10 +6409,10 @@
constexpr iterator_t<@\exposid{Base}@> base() &&;

constexpr decltype(auto) operator*() const
{ return get<N>(*@\exposid{current_}@); }
{ return @\exposid{get-element}@(@\exposid{current_}@); }

constexpr @\exposid{iterator}@& operator++();
constexpr void operator++(int) requires (!@\libconcept{forward_range}@<@\exposid{Base}@>);
constexpr void operator++(int);
constexpr @\exposid{iterator}@ operator++(int) requires @\libconcept{forward_range}@<@\exposid{Base}@>;

constexpr @\exposid{iterator}@& operator--() requires @\libconcept{bidirectional_range}@<@\exposid{Base}@>;
Expand All @@ -6409,7 +6425,7 @@

constexpr decltype(auto) operator[](difference_type n) const
requires @\libconcept{random_access_range}@<@\exposid{Base}@>
{ return get<N>(*(@\exposid{current_}@ + n)); }
{ return @\exposid{get-element}@(@\exposid{current_}@ + n); }

friend constexpr bool operator==(const @\exposid{iterator}@& x, const @\exposid{iterator}@& y)
requires @\libconcept{equality_comparable}@<iterator_t<@\exposid{Base}@>>;
Expand Down Expand Up @@ -6437,6 +6453,25 @@
}
\end{codeblock}

\indexlibrarymember{\exposid{get-element}}{elements_view::iterator}%
\begin{itemdecl}
static constexpr decltype(auto) @\exposid{get-element}@(const iterator_t<@\exposid{Base}@>& i); // \expos
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to:
\begin{codeblock}
if constexpr (is_reference_v<range_reference_t<@\exposid{Base}@>>) {
return get<N>(*i);
} else {
using E = remove_cv_t<tuple_element_t<N, range_reference_t<@\exposid{Base}@>>>;
return static_cast<E>(get<N>(*i));
}
\end{codeblock}
\end{itemdescr}

\indexlibraryctor{elements_view::iterator}%
\begin{itemdecl}
constexpr explicit @\exposid{iterator}@(iterator_t<@\exposid{Base}@> current);
Expand Down Expand Up @@ -6500,7 +6535,7 @@

\indexlibrarymember{operator++}{elements_view::iterator}%
\begin{itemdecl}
constexpr void operator++(int) requires (!@\libconcept{forward_range}@<@\exposid{Base}@>);
constexpr void operator++(int);
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -6715,7 +6750,8 @@
namespace std::ranges {
template<@\libconcept{input_range}@ V, size_t N>
requires @\libconcept{view}@<V> && @\placeholder{has-tuple-element}@<range_value_t<V>, N> &&
@\placeholder{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N>
@\placeholder{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N> &&
@\exposconcept{returnable-element}@<range_reference_t<V>, N>
template<bool Const>
class elements_view<V, N>::@\exposid{sentinel}@ { // \expos
private:
Expand Down
4 changes: 2 additions & 2 deletions source/support.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -3020,8 +3020,8 @@
\remarks
An invocation of this function
may be used in a core constant expression
whenever the value of its argument
may be used in a core constant expression.
if and only if the (converted) value of its argument
may be used in place of the function invocation.
A byte of storage \placeholder{b} is
reachable through a pointer value
that points to an object \placeholder{Y}
Expand Down