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[2026-03 LWG Motion 27] P3842R2 A conservative fix for constexpr uncaught_exceptions() and current_exception() #8906

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[2026-03 LWG Motion 27] P3842R2 A conservative fix for constexpr uncaught_exceptions() and current_exception() #8906

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48 changes: 22 additions & 26 deletions source/support.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -3837,18 +3837,19 @@
terminate_handler set_terminate(terminate_handler f) noexcept;
[[noreturn]] void terminate() noexcept;

constexpr int uncaught_exceptions() noexcept;
int uncaught_exceptions() noexcept;

using exception_ptr = @\unspec@;

constexpr exception_ptr current_exception() noexcept;
constexpr exception_ptr @\exposid{current-exception}@() noexcept; // \expos
exception_ptr current_exception() noexcept;
[[noreturn]] constexpr void rethrow_exception(exception_ptr p);
template<class E> constexpr exception_ptr make_exception_ptr(E e) noexcept;
template<class E> constexpr const E* exception_ptr_cast(const exception_ptr& p) noexcept;
template<class E> void exception_ptr_cast(const exception_ptr&&) = delete;

template<class T> [[noreturn]] constexpr void throw_with_nested(T&& t);
template<class E> constexpr void rethrow_if_nested(const E& e);
template<class T> [[noreturn]] void throw_with_nested(T&& t);
template<class E> void rethrow_if_nested(const E& e);
}
\end{codeblock}

Expand Down Expand Up @@ -4073,7 +4074,7 @@

\indexlibraryglobal{uncaught_exceptions}%
\begin{itemdecl}
constexpr int uncaught_exceptions() noexcept;
int uncaught_exceptions() noexcept;
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -4142,7 +4143,8 @@

\indexlibraryglobal{current_exception}%
\begin{itemdecl}
constexpr exception_ptr current_exception() noexcept;
constexpr exception_ptr @\exposid{current-exception}@() noexcept;
exception_ptr current_exception() noexcept;
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -4212,15 +4214,9 @@
try {
throw e;
} catch(...) {
return current_exception();
return @\exposid{current-exception}@();
}
\end{codeblock}

\pnum
\begin{note}
This function is provided for convenience and
efficiency reasons.
\end{note}
\end{itemdescr}

\indexlibraryglobal{exception_ptr_cast}%
Expand Down Expand Up @@ -4256,18 +4252,18 @@
namespace std {
class nested_exception {
public:
constexpr nested_exception() noexcept;
constexpr nested_exception(const nested_exception&) noexcept = default;
constexpr nested_exception& operator=(const nested_exception&) noexcept = default;
constexpr virtual ~nested_exception() = default;
nested_exception() noexcept;
nested_exception(const nested_exception&) noexcept = default;
nested_exception& operator=(const nested_exception&) noexcept = default;
virtual ~nested_exception() = default;

// access functions
[[noreturn]] constexpr void rethrow_nested() const;
constexpr exception_ptr nested_ptr() const noexcept;
[[noreturn]] void rethrow_nested() const;
exception_ptr nested_ptr() const noexcept;
};

template<class T> [[noreturn]] constexpr void throw_with_nested(T&& t);
template<class E> constexpr void rethrow_if_nested(const E& e);
template<class T> [[noreturn]] void throw_with_nested(T&& t);
template<class E> void rethrow_if_nested(const E& e);
}
\end{codeblock}

Expand All @@ -4284,7 +4280,7 @@

\indexlibraryctor{nested_exception}%
\begin{itemdecl}
constexpr nested_exception() noexcept;
nested_exception() noexcept;
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -4295,7 +4291,7 @@

\indexlibrarymember{rethrow_nested}{nested_exception}%
\begin{itemdecl}
[[noreturn]] constexpr void rethrow_nested() const;
[[noreturn]] void rethrow_nested() const;
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -4307,7 +4303,7 @@

\indexlibrarymember{nested_ptr}{nested_exception}%
\begin{itemdecl}
constexpr exception_ptr nested_ptr() const noexcept;
exception_ptr nested_ptr() const noexcept;
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -4318,7 +4314,7 @@

\indexlibrarymember{throw_with_nested}{nested_exception}%
\begin{itemdecl}
template<class T> [[noreturn]] constexpr void throw_with_nested(T&& t);
template<class T> [[noreturn]] void throw_with_nested(T&& t);
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -4341,7 +4337,7 @@

\indexlibrarymember{rethrow_if_nested}{nested_exception}%
\begin{itemdecl}
template<class E> constexpr void rethrow_if_nested(const E& e);
template<class E> void rethrow_if_nested(const E& e);
\end{itemdecl}

\begin{itemdescr}
Expand Down
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