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P3138R5 views::cache_latest
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@jensmaurer
jensmaurer committed Dec 6, 2024
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329 changes: 328 additions & 1 deletion source/ranges.tex
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class cartesian_product_view; // freestanding

namespace views { inline constexpr @\unspecnc@ cartesian_product = @\unspecnc@; } // freestanding

// \ref{range.cache.latest}, cache latest view
template<input_range V>
requires view<V>
class cache_latest_view;

namepspace views { inline constexpr @\unspec@ cache_latest = @\unspec@; }
}

namespace std {
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\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{++*this;}
Equivalent to \tcode{++*this;}
\end{itemdescr}

\indexlibrarymember{operator++}{stride_view::\exposid{iterator}}%
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\end{itemize}
\end{itemdescr}

\rSec2[range.cache.latest]{Cache latest view}

\rSec3[range.cache.latest.overview]{Overview}

\pnum
\tcode{cache_latest_view} caches the last-accessed element of
its underlying sequence
so that the element does not have to be recomputed on repeated access.
\begin{note}
This is useful if computation of the element to produce is expensive.
\end{note}

\pnum
The name \tcode{views::cache_latest} denotes
a range adaptor object\iref{range.adaptor.object}.
Let \tcode{E} be an expression.
The expression \tcode{views::cache_latest(E)} is expression-equivalent to
\tcode{cache_latest_view(E)}.

\rSec3[range.cache.latest.view]{Class template \tcode{cache_latest_view}}

\begin{codeblock}
namespace std::ranges {
template<@\libconcept{input_range}@ V>
requires @\libconcept{view}@<V>
class cache_latest_view : public view_interface<cache_latest_view<V>> {
V @\exposid{base_}@ = V(); // \expos
using @\exposid{cache_t}@ = conditional_t<is_reference_v<range_reference_t<V>>, // \expos
add_pointer_t<range_reference_t<V>>,
range_reference_t<V>>;

@\exposid{non-propagating-cache}@<cache_t> @\exposid{cache_}@; // \expos

class @\exposid{iterator}@; // \expos
class @\exposid{sentinel}@; // \expos

public:
cache_latest_view() requires @\libconcept{default_initializable}@<V> = default;
constexpr explicit cache_latest_view(V base);

constexpr V base() const & requires @\libconcept{copy_constructible}@<V> { return @\exposid{base_}@; }
constexpr V base() && { return std::move(@\exposid{base_}@); }

constexpr auto begin();
constexpr auto end();

constexpr auto size() requires @\libconcept{sized_range}@<V>;
constexpr auto size() const requires @\libconcept{sized_range}@<const V>;
};

template<class R>
cache_latest_view(R&&) -> cache_latest_view<views::all_t<R>>;
}
\end{codeblock}

\begin{itemdecl}
constexpr explicit cache_latest_view(V base);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Initializes \exposid{base_} with \tcode{std::move(base)}.
\end{itemdescr}

\begin{itemdecl}
constexpr auto begin();
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return \exposid{iterator}(*this);}
\end{itemdescr}

\begin{itemdecl}
constexpr auto end();
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return \exposid{sentinel}(*this);}
\end{itemdescr}

\begin{itemdecl}
constexpr auto size() requires sized_range<V>;
constexpr auto size() const requires sized_range<const V>;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return ranges::size(\exposid{base_});}
\end{itemdescr}

\rSec3[range.cache.latest.iterator]{Class \tcode{cache_latest_view::\exposid{iterator}}}

\begin{codeblock}
namespace std::ranges {
template<@\libconcept{input_range}@ V>
requires @\libconcept{view}@<V>
class cache_latest_view<V>::@\exposid{iterator}@ {
cache_latest_view* @\exposid{parent_}@; // \expos
iterator_t<V> @\exposid{current_}@; // \expos

constexpr explicit @\exposid{iterator}@(cache_latest_view& parent); // \expos

public:
using difference_type = range_difference_t<V>;
using value_type = range_value_t<V>;
using iterator_concept = input_iterator_tag;

@\exposid{iterator}@(@\exposid{iterator}@&&) = default;
@\exposid{iterator}@& operator=(@\exposid{iterator}@&&) = default;

constexpr iterator_t<V> base() &&;
constexpr const iterator_t<V>& base() const & noexcept;

constexpr range_reference_t<V>& operator*() const;

constexpr @\exposid{iterator}@& operator++();
constexpr void operator++(int);

friend constexpr range_rvalue_reference_t<V> iter_move(const @\exposid{iterator}@& i)
noexcept(noexcept(ranges::iter_move(i.@\exposid{current_}@)));

friend constexpr void iter_swap(const @\exposid{iterator}@& x, const @\exposid{iterator}@& y)
noexcept(noexcept(ranges::iter_swap(x.@\exposid{current_}@, y.@\exposid{current_}@)))
requires @\libconcept{indirectly_swappable}@<iterator_t<V>>;
};
}
\end{codeblock}

\begin{itemdecl}
constexpr explicit @\exposid{iterator}@(cache_latest_view& parent);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Initializes \exposid{current_} with
\tcode{ranges::begin(parent.\exposid{base_})}
and \exposid{parent_} with \tcode{addressof(parent)}.
\end{itemdescr}

\begin{itemdecl}
constexpr iterator_t<V> base() &&;
\end{itemdecl}

\begin{itemdescr}
\pnum
\returns
\tcode{std::move(\exposid{current_})}.
\end{itemdescr}

\begin{itemdecl}
constexpr const iterator_t<V>& base() const & noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\returns
\exposid{current_}.
\end{itemdescr}

\begin{itemdecl}
constexpr iterator& operator++();
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to:
\begin{codeblock}
@\exposid{parent_}@->@\exposid{cache_}@.reset();
++@\exposid{current_}@;
return *this;
\end{codeblock}
\end{itemdescr}

\begin{itemdecl}
constexpr void operator++(int);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{++*this}.
\end{itemdescr}

\begin{itemdecl}
constexpr range_reference_t<V>& operator*() const;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to:
\begin{codeblock}
if constexpr (is_reference_v<range_reference_t<V>>) {
if (!@\exposid{parent_}@->@\exposid{cache_}@) {
@\exposid{parent_}@->@\exposid{cache_}@ = addressof(@\exposid{as-lvalue}@(*@\exposid{current_}@));
}
return **@\exposid{parent_}@->@\exposid{cache_}@;
} else {
if (!@\exposid{parent_}@->c@\exposid{ache_}@) {
@\exposid{parent_}@->@\exposid{cache_}@.@\exposid{emplace-deref}@(@\exposid{current_}@);
}
return *@\exposid{parent_}@->@\exposid{cache_}@;
}
\end{codeblock}
\begin{note}
Evaluations of \tcode{operator*} on the same iterator object
can conflict\iref{intro.races}.
\end{note}
\end{itemdescr}

\begin{itemdecl}
friend constexpr range_rvalue_reference_t<V> iter_move(const @\exposid{iterator}@& i)
noexcept(noexcept(ranges::iter_move(i.@\exposid{current_}@)));
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return ranges::iter_move(i.\exposid{current_});}
\end{itemdescr}

\begin{itemdecl}
friend constexpr void iter_swap(const @\exposid{iterator}@& x, const @\exposid{iterator}@& y)
noexcept(noexcept(ranges::iter_swap(x.@\exposid{current_}@, y.@\exposid{current_}@)))
requires @\libconcept{indirectly_swappable}@<iterator_t<V>>;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to
\tcode{ranges::iter_swap(x.\exposid{current_}, y.\exposid{current_})}.
\end{itemdescr}

\rSec3[range.cache.latest.sentinel]{Class \tcode{cache_latest_view::\exposid{sentinel}}}

\begin{codeblock}
namespace std::ranges {
template<@\libconcept{input_range}@ V>
requires @\libconcept{view}@<V>
class cache_latest_view<V>::@\exposid{sentinel}@ {
sentinel_t<V> @\exposid{end_}@ = sentinel_t<V>(); // \expos

constexpr explicit @\exposid{sentinel}@(cache_latest_view& parent); // \expos

public:
@\exposid{sentinel}@() = default;

constexpr sentinel_t<V> base() const;

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

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

\begin{itemdecl}
constexpr explicit @\exposid{sentinel}@(cache_latest_view& parent);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Initializes \exposid{end_} with \tcode{ranges::end(parent.\exposid{base_})}.
\end{itemdescr}

\begin{itemdecl}
constexpr sentinel_t<V> base() const;
\end{itemdecl}

\begin{itemdescr}
\pnum
\returns
\exposid{end_}.
\end{itemdescr}

\begin{itemdecl}
friend constexpr bool operator==(const iterator& x, const sentinel& y);
\end{itemdecl}

\begin{itemdescr}
\pnum
\returns
\tcode{x.\exposid{current_} == y.\exposid{end_}}.
\end{itemdescr}

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

\begin{itemdescr}
\pnum
\returns
\tcode{x.\exposid{current_} - y.\exposid{end_}}.
\end{itemdescr}

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

\begin{itemdescr}
\pnum
\returns
\tcode{x.\exposid{end_} - y.\exposid{current_}}.
\end{itemdescr}

\rSec1[coro.generator]{Range generators}

\rSec2[coroutine.generator.overview]{Overview}
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1 change: 1 addition & 0 deletions source/support.tex
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Expand Up @@ -739,6 +739,7 @@
// also in \libheader{algorithm}, \libheader{functional}, \libheader{iterator}, \libheader{memory}, \libheader{ranges}
#define @\defnlibxname{cpp_lib_ranges_as_const}@ 202311L // freestanding, also in \libheader{ranges}
#define @\defnlibxname{cpp_lib_ranges_as_rvalue}@ 202207L // freestanding, also in \libheader{ranges}
#define @\defnlibxname{cpp_lib_ranges_cache_latest}@ 202411L // also in \libheader{ranges}
#define @\defnlibxname{cpp_lib_ranges_cartesian_product}@ 202207L // freestanding, also in \libheader{ranges}
#define @\defnlibxname{cpp_lib_ranges_chunk}@ 202202L // freestanding, also in \libheader{ranges}
#define @\defnlibxname{cpp_lib_ranges_chunk_by}@ 202202L // freestanding, also in \libheader{ranges}
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