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[2026-06 LWG Motion 5] P4206R0 Revert string support in std::constant_wrapper #9125

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[2026-06 LWG Motion 5] P4206R0 Revert string support in std::constant_wrapper #9125

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2 changes: 1 addition & 1 deletion source/support.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -620,7 +620,7 @@
#define @\defnlibxname{cpp_lib_complex_udls}@ 201309L // also in \libheader{complex}
#define @\defnlibxname{cpp_lib_concepts}@ 202207L
// freestanding, also in \libheader{concepts}, \libheader{compare}
#define @\defnlibxname{cpp_lib_constant_wrapper}@ 202603L // freestanding, also in \libheader{utility}
#define @\defnlibxname{cpp_lib_constant_wrapper}@ 202606L // freestanding, also in \libheader{utility}
#define @\defnlibxname{cpp_lib_constexpr_algorithms}@ 202306L // also in \libheader{algorithm}, \libheader{utility}
#define @\defnlibxname{cpp_lib_constexpr_atomic}@ 202411L // also in \libheader{atomic}
#define @\defnlibxname{cpp_lib_constexpr_bitset}@ 202207L // also in \libheader{bitset}
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45 changes: 9 additions & 36 deletions source/utilities.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -98,10 +98,7 @@
void observable_checkpoint() noexcept;

// \ref{const.wrap.class}, class template \tcode{constant_wrapper}
template<class T>
struct @\exposidnc{cw-fixed-value}@; // \expos

template<@\exposidnc{cw-fixed-value}@ X, class = typename decltype(X)::@\exposid{type}@>
template<auto X, class = decltype(X)>
struct constant_wrapper;

template<class T>
Expand All @@ -110,7 +107,7 @@

struct @\exposidnc{cw-operators}@; // \expos

template<@\exposid{cw-fixed-value}@ X>
template<auto X>
constexpr auto @\libglobal{cw}@ = constant_wrapper<X>{};

// \ref{intseq}, compile-time integer sequences%
Expand Down Expand Up @@ -754,23 +751,6 @@

\begin{codeblock}
namespace std {
template<class T>
struct @\exposidnc{cw-fixed-value}@ { // \expos
using @\exposidnc{type}@ = T; // \expos
constexpr @\exposidnc{cw-fixed-value}@(@\exposidnc{type}@ v) noexcept : @\exposidnc{data}@(v) {}
T @\exposidnc{data}@; // \expos
};

template<class T, size_t Extent>
struct @\exposidnc{cw-fixed-value}@<T[Extent]> { // \expos
using @\exposidnc{type}@ = T[Extent]; // \expos
constexpr @\exposidnc{cw-fixed-value}@(T (&arr)[Extent]) noexcept;
T @\exposidnc{data}@[Extent]; // \expos
};

template<class T, size_t Extent>
@\exposidnc{cw-fixed-value}@(T (&)[Extent]) -> @\exposidnc{cw-fixed-value}@<T[Extent]>; // \expos

struct @\exposidnc{cw-operators}@ { // \expos
// unary operators
template<@\exposconcept{constexpr-param}@ T>
Expand Down Expand Up @@ -914,11 +894,11 @@
-> constant_wrapper<(T::value >>= R::value)> { return {}; }
};

template<@\exposid{cw-fixed-value}@ X, class>
template<auto X, class T>
struct @\libglobal{constant_wrapper}@ : @\exposid{cw-operators}@ {
static constexpr const auto & value = X.@\exposid{data}@;
static constexpr decltype(auto) value = (X);
using type = constant_wrapper;
using value_type = decltype(X)::@\exposid{type}@;
using value_type = decltype(X);

template<@\exposconcept{constexpr-param}@ R>
constexpr auto operator=(R) const noexcept
Expand All @@ -943,8 +923,11 @@
that are passed as arguments to constexpr functions to be used in constant expressions.

\pnum
If a specialization of \tcode{constant_wrapper} is instantiated with a type \tcode{T}
such that \tcode{is_same_v<T, value_type>} is \tcode{false},
the program is ill-formed.
\begin{note}
The unnamed second template parameter to \tcode{constant_wrapper} is present
The second template parameter to \tcode{constant_wrapper} is present
to aid argument-dependent lookup\iref{basic.lookup.argdep}
in finding overloads for which \tcode{constant_wrapper}'s wrapped value is a suitable argument,
but for which the \tcode{constant_wrapper} itself is not.
Expand Down Expand Up @@ -982,16 +965,6 @@
\end{codeblock}
\end{example}

\begin{itemdecl}
constexpr @\exposid{cw-fixed-value}@(T (&arr)[Extent]) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Initialize elements of \exposid{data} with corresponding elements of \tcode{arr}.
\end{itemdescr}

\indexlibrarymember{operator()}{constant_wrapper}%
\begin{itemdecl}
template<class... Args>
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