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[2026-06 LWG Motion 4] P3052R2 (view_interface::at()) #9126

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[2026-06 LWG Motion 4] P3052R2 (view_interface::at()) #9126

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P3052R2 view_interface::at()
eisenwave Jun 14, 2026
9aa96fa
Fixup: Add missing "is true"
eisenwave Jun 14, 2026
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26 changes: 25 additions & 1 deletion source/ranges.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -138,7 +138,7 @@
// \ref{view.interface}, class template \tcode{view_interface}
template<class D>
requires is_class_v<D> && @\libconcept{same_as}@<D, remove_cv_t<D>>
class view_interface;
class view_interface; // partially freestanding

@jwakely jwakely Jun 23, 2026

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Hmm, the paper shows "freestanding" as already present, but it isn't.

Ah the // freestanding comment was removed by LWG4189. So this edit is the correct way to resolve the merge conflict.


// \ref{range.subrange}, sub-ranges
enum class @\libglobal{subrange_kind}@ : bool { @\libmember{unsized}{subrange_kind}@, @\libmember{sized}{subrange_kind}@ };
Expand Down Expand Up @@ -1868,6 +1868,11 @@
constexpr decltype(auto) operator[](range_difference_t<R> n) const {
return ranges::begin(@\exposid{derived}@())[n];
}

template<@\libconcept{random_access_range}@ R = D> requires @\libconcept{sized_range}@<R> // freestanding-deleted
constexpr decltype(auto) at(range_difference_t<R> n);
template<@\libconcept{random_access_range}@ R = const D> requires @\libconcept{sized_range}@<R> // freestanding-deleted
constexpr decltype(auto) at(range_difference_t<R> n) const;
};
}
\end{codeblock}
Expand Down Expand Up @@ -1914,6 +1919,25 @@
Equivalent to: \tcode{return *ranges::prev(ranges::end(\exposid{derived}()));}
\end{itemdescr}

\indexlibrarymember{at}{view_interface}%
\begin{itemdecl}
template<@\libconcept{random_access_range}@ R = D> requires @\libconcept{sized_range}@<R>
constexpr decltype(auto) at(range_difference_t<R> n);
template<@\libconcept{random_access_range}@ R = const D> requires @\libconcept{sized_range}@<R>
constexpr decltype(auto) at(range_difference_t<R> n) const;
\end{itemdecl}

\begin{itemdescr}
\pnum
\returns
\tcode{(*this)[n]}.

\pnum
\throws
\tcode{out_of_range} if \tcode{n < 0} is \tcode{true} or
\tcode{n >= ranges::distance(\exposid{derived}())} is \tcode{true}.

@jwakely jwakely Jun 24, 2026

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Correct additions of "is true" which was missing from the incoming paper.

\end{itemdescr}

\rSec2[range.subrange]{Sub-ranges}

\rSec3[range.subrange.general]{General}
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1 change: 1 addition & 0 deletions source/support.tex
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Expand Up @@ -885,6 +885,7 @@
#define @\defnlibxname{cpp_lib_unwrap_ref}@ 201811L // freestanding, also in \libheader{type_traits}
#define @\defnlibxname{cpp_lib_valarray}@ 202511L // also in \libheader{valarray}
#define @\defnlibxname{cpp_lib_variant}@ 202306L // also in \libheader{variant}
#define @\defnlibxname{cpp_lib_view_interface}@ 202606L // also in \libheader{ranges}
#define @\defnlibxname{cpp_lib_void_t}@ 201411L // freestanding, also in \libheader{type_traits}
\end{codeblock}

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