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LWG Poll 13: P1994R1 elements_view needs its own sentinel #3754

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Merged
merged 2 commits into from
Feb 29, 2020
Merged

LWG Poll 13: P1994R1 elements_view needs its own sentinel #3754

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517f76f
P1994R1 elements_view needs its own sentinel
Feb 19, 2020
eff9794
[range.elements.sentinel] Fix template-head for elements_view::sentin…
Feb 24, 2020
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134 changes: 101 additions & 33 deletions source/ranges.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -6036,11 +6036,17 @@
constexpr auto begin() const requires @\placeholder{simple-view}@<V>
{ return @\exposid{iterator}@<true>(ranges::begin(@\exposid{base_}@)); }

constexpr auto end() requires (!@\placeholder{simple-view}@<V>)
{ return ranges::end(@\exposid{base_}@); }
constexpr auto end()
{ return @\exposid{sentinel}@<false>{ranges::end(@\exposid{base_}@)}; }

constexpr auto end() const requires @\placeholder{simple-view}@<V>
{ return ranges::end(@\exposid{base_}@); }
constexpr auto end() requires common_range<V>
{ return @\exposid{iterator}@<false>{ranges::end(@\exposid{base_}@)}; }

constexpr auto end() const requires range<const V>
{ return @\exposid{sentinel}@<true>{ranges::end(@\exposid{base_}@)}; }

constexpr auto end() const requires common_range<const V>
{ return @\exposid{iterator}@<true>{ranges::end(@\exposid{base_}@)}; }

constexpr auto size() requires sized_range<V>
{ return ranges::size(@\exposid{base_}@); }
Expand All @@ -6050,6 +6056,8 @@

private:
template<bool> struct @\exposid{iterator}@; // \expos
// \ref{range.elements.sentinel}, class template \tcode{elements_view::\exposid{sentinel}}
template<bool> struct @\exposid{sentinel}@; // \expos
V @\exposid{base_}@ = V(); // \expos
};
}
Expand Down Expand Up @@ -6112,7 +6120,6 @@

friend constexpr bool operator==(const @\exposid{iterator}@& x, const @\exposid{iterator}@& y)
requires equality_comparable<iterator_t<@\exposid{base-t}@>>;
friend constexpr bool operator==(const @\exposid{iterator}@& x, const sentinel_t<@\exposid{base-t}@>& y);

friend constexpr bool operator<(const @\exposid{iterator}@& x, const @\exposid{iterator}@& y)
requires random_access_range<@\exposid{base-t}@>;
Expand All @@ -6133,13 +6140,6 @@
requires random_access_range<@\exposid{base-t}@>;
friend constexpr difference_type operator-(const @\exposid{iterator}@& x, const @\exposid{iterator}@& y)
requires random_access_range<@\exposid{base-t}@>;

friend constexpr difference_type
operator-(const @\exposid{iterator}@<Const>& x, const sentinel_t<@\exposid{base-t}@>& y)
requires sized_sentinel_for<sentinel_t<@\exposid{base-t}@>, iterator_t<@\exposid{base-t}@>>;
friend constexpr difference_type
operator-(const sentinel_t<@\exposid{base-t}@>& x, const @\exposid{iterator}@<Const>& y)
requires sized_sentinel_for<sentinel_t<@\exposid{base-t}@>, iterator_t<@\exposid{base-t}@>>;
};
}
\end{codeblock}
Expand Down Expand Up @@ -6307,17 +6307,6 @@
Equivalent to: \tcode{return x.\exposid{current_} == y.\exposid{current_};}
\end{itemdescr}

\indexlibrarymember{operator==}{elements_view::iterator}%
\begin{itemdecl}
friend constexpr bool operator==(const @\exposid{iterator}@& x, const sentinel_t<@\exposid{base-t}@>& y);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return x.\exposid{current_} == y;}
\end{itemdescr}

\indexlibrarymember{operator<}{elements_view::iterator}%
\begin{itemdecl}
friend constexpr bool operator<(const @\exposid{iterator}@& x, const @\exposid{iterator}@& y)
Expand Down Expand Up @@ -6426,28 +6415,107 @@
Equivalent to: \tcode{return x.\exposid{current_} - y.\exposid{current_};}
\end{itemdescr}

\indexlibrarymember{operator-}{elements_view::iterator}%
\rSec3[range.elements.sentinel]{Class template \tcode{elements_view::\exposid{sentinel}}}

\indexlibraryglobal{elements_view::sentinel}%
\begin{codeblock}
namespace std::ranges {
template<input_range V, size_t N>
requires view<V> && @\placeholder{has-tuple-element}@<range_value_t<V>, N> &&
@\placeholder{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N>
template<bool Const>
class elements_view<V, N>::@\exposid{sentinel}@ { // \expos
private:
using @\exposid{Base}@ = conditional_t<Const, const V, V>; // \expos
sentinel_t<@\exposid{Base}@> @\exposid{end_}@ = sentinel_t<@\exposid{Base}@>(); // \expos
public:
@\exposid{sentinel}@() = default;
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end);
constexpr @\exposid{sentinel}@(@\exposid{sentinel}@<!Const> other)
requires Const && convertible_to<sentinel_t<V>, sentinel_t<@\exposid{Base}@>>;

constexpr sentinel_t<@\exposid{Base}@> base() const;

friend constexpr bool operator==(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y);

friend constexpr range_difference_t<@\exposid{Base}@>
operator-(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y)
requires sized_sentinel_for<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;

friend constexpr range_difference_t<@\exposid{Base}@>
operator-(const @\exposid{sentinel}@& x, const @\exposid{iterator}@<Const>& y)
requires sized_sentinel_for<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
};
}
\end{codeblock}

\indexlibraryctor{elements_view::sentinel}%
\begin{itemdecl}
friend constexpr difference_type
operator-(const @\exposid{iterator}@<Const>& x, const sentinel_t<@\exposid{base-t}@>& y)
requires sized_sentinel_for<sentinel_t<@\exposid{base-t}@>, iterator_t<@\exposid{base-t}@>>;
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return x.\exposid{current_} - y;}
Initializes \exposid{end_} with \tcode{end}.
\end{itemdescr}

\indexlibrarymember{operator-}{elements_view::iterator}%
\indexlibraryctor{elements_view::sentinel}%
\begin{itemdecl}
friend constexpr difference_type
operator-(const sentinel_t<@\exposid{base-t}@>& x, const @\exposid{iterator}@<Const>& y)
requires sized_sentinel_for<sentinel_t<@\exposid{base-t}@>, iterator_t<@\exposid{base-t}@>>;
constexpr @\exposid{sentinel}@(@\exposid{sentinel}@<!Const> other)
requires Const && convertible_to<sentinel_t<V>, sentinel_t<@\exposid{Base}@>>;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return -(y - x);}
Initializes \exposid{end_} with \tcode{std::move(other.\exposid{end_})}.
\end{itemdescr}

\indexlibrarymember{base}{elements_view::sentinel}%
\begin{itemdecl}
constexpr sentinel_t<@\exposid{Base}@> base() const;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return \exposid{end_};}
\end{itemdescr}

\indexlibrarymember{operator==}{elements_view::sentinel}%
\begin{itemdecl}
friend constexpr bool operator==(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return x.\exposid{current_} == y.\exposid{end_};}
\end{itemdescr}

\indexlibrarymember{operator-}{elements_view::sentinel}%
\begin{itemdecl}
friend constexpr range_difference_t<@\exposid{Base}@>
operator-(const @\exposid{iterator}@<Const>& x, const @\exposid{sentinel}@& y)
requires sized_sentinel_for<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return x.\exposid{current_} - y.\exposid{end_};}
\end{itemdescr}

\indexlibrarymember{operator-}{elements_view::sentinel}%
\begin{itemdecl}
friend constexpr range_difference_t<@\exposid{Base}@>
operator-(const @\exposid{sentinel}@& x, const @\exposid{iterator}@<Const>& y)
requires sized_sentinel_for<sentinel_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return x.\exposid{end_} - y.\exposid{current_};}
\end{itemdescr}