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P3913R1 Optimize for std::optional in range adaptors #8543

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P3913R1 Optimize for std::optional in range adaptors #8543

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P3913R1 Optimize for std::optional in range adaptors
steve-downey Nov 11, 2025
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steve-downey Nov 16, 2025
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20 changes: 20 additions & 0 deletions source/ranges.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -5898,6 +5898,11 @@
except that the evaluations of \tcode{E} and \tcode{F}
are indeterminately sequenced.

\item
Otherwise, if \tcode{T} is a specialization of
\tcode{optional} and \tcode{T} models \libconcept{view}, then
\tcode{(static_cast<D>(F) == D() ? ((void)E, T()) : \exposidnc{decay-copy}(E))}.

\item
Otherwise, if \tcode{T} models
\libconcept{random_access_range} and \libconcept{sized_range}
Expand Down Expand Up @@ -6381,6 +6386,11 @@
except that the evaluations of \tcode{E} and \tcode{F}
are indeterminately sequenced.

\item
Otherwise, if \tcode{T} is a specialization of \tcode{optional}
and \tcode{T} models \libconcept{view}, then
\tcode{(static_cast<D>(F) == D() ? \exposidnc{decay-copy}(E) : ((void)E, T()))}.

\item
Otherwise, if \tcode{T} models
\libconcept{random_access_range} and \libconcept{sized_range}
Expand Down Expand Up @@ -9909,6 +9919,11 @@
If the type of \tcode{E} is
a (possibly cv-qualified) specialization of \tcode{reverse_view},
then \tcode{E.base()}.

\item
Otherwise, if \tcode{E} is specialization of \tcode{optional} and \tcode{E}
models \libconcept{view}, then \tcode{\exposidnc{decay-copy}(E)}.

\item
Otherwise, if the type of \tcode{E} is \cv{} \tcode{subrange<reverse_iterator<I>, reverse_iterator<I>, K>}
for some iterator type \tcode{I} and
Expand Down Expand Up @@ -10060,6 +10075,11 @@
Otherwise,
if \tcode{U} denotes \tcode{empty_view<X>}
for some type \tcode{X}, then \tcode{auto(views::empty<const X>)}.

\item
Otherwise, if \tcode{U} denotes \tcode{optional<X\&>}
for some type \tcode{X}, then \tcode{optional<const X\&>(E)}.

\item
Otherwise,
if \tcode{U} denotes \tcode{span<X, Extent>}
Expand Down