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P3068R6 Allowing exception throwing in constant-evaluation #7438

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Dec 16, 2024
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P3068R6 Allowing exception throwing in constant-evaluation #7438

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20 changes: 15 additions & 5 deletions source/expressions.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -7878,6 +7878,13 @@
unless it deallocates a region of storage
allocated within the evaluation of $E$;

\item
a construction of an exception object,
unless the exception object and
all of its implicit copies created by invocations of
\tcode{std::current_exception} or \tcode{std::rethrow_exception}\iref{propagation}
are destroyed within the evaluation of $E$;

\item
an \grammarterm{await-expression}\iref{expr.await};

Expand All @@ -7889,15 +7896,18 @@
relational\iref{expr.rel}, or equality\iref{expr.eq}
operator where the result is unspecified;

\item
a \grammarterm{throw-expression}\iref{expr.throw};

\item
a \keyword{dynamic_cast}\iref{expr.dynamic.cast} or
\keyword{typeid}\iref{expr.typeid} expression
on a glvalue that refers to an object
whose dynamic type is constexpr-unknown or
that would throw an exception;
whose dynamic type is constexpr-unknown;

\item
a \tcode{dynamic_cast}\iref{expr.dynamic.cast} expression,
\tcode{typeid}\iref{expr.typeid} expression, or
\tcode{new-expression}\iref{expr.new}
that would throw an exception
where no definition of the exception type is reachable;

\item
an \grammarterm{asm-declaration}\iref{dcl.asm};
Expand Down
1 change: 1 addition & 0 deletions source/preprocessor.tex
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Expand Up @@ -1859,6 +1859,7 @@
\defnxname{cpp_conditional_explicit} & \tcode{201806L} \\ \rowsep
\defnxname{cpp_constexpr} & \tcode{202406L} \\ \rowsep
\defnxname{cpp_constexpr_dynamic_alloc} & \tcode{201907L} \\ \rowsep
\defnxname{cpp_constexpr_exceptions} & \tcode{202411L} \\ \rowsep
\defnxname{cpp_constexpr_in_decltype} & \tcode{201711L} \\ \rowsep
\defnxname{cpp_consteval} & \tcode{202211L} \\ \rowsep
\defnxname{cpp_constinit} & \tcode{201907L} \\ \rowsep
Expand Down
92 changes: 49 additions & 43 deletions source/support.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -607,6 +607,7 @@
#define @\defnlibxname{cpp_lib_constexpr_cmath}@ 202306L // also in \libheader{cmath}, \libheader{cstdlib}
#define @\defnlibxname{cpp_lib_constexpr_complex}@ 202306L // also in \libheader{complex}
#define @\defnlibxname{cpp_lib_constexpr_dynamic_alloc}@ 201907L // also in \libheader{memory}
#define @\defnlibxname{cpp_lib_constexpr_exceptions}@ 202411L // also in \libheader{exception}
#define @\defnlibxname{cpp_lib_constexpr_functional}@ 201907L // freestanding, also in \libheader{functional}
#define @\defnlibxname{cpp_lib_constexpr_iterator}@ 201811L // freestanding, also in \libheader{iterator}
#define @\defnlibxname{cpp_lib_constexpr_memory}@ 202202L // freestanding, also in \libheader{memory}
Expand Down Expand Up @@ -2941,7 +2942,7 @@
class bad_alloc : public exception {
public:
// see \ref{exception} for the specification of the special member functions
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
};
}
\end{codeblock}
Expand All @@ -2954,7 +2955,7 @@

\indexlibrarymember{what}{bad_alloc}%
\begin{itemdecl}
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -2972,7 +2973,7 @@
class bad_array_new_length : public bad_alloc {
public:
// see \ref{exception} for the specification of the special member functions
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
};
}
\end{codeblock}
Expand All @@ -2985,7 +2986,7 @@

\indexlibrarymember{what}{bad_array_new_length}%
\begin{itemdecl}
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -3310,7 +3311,7 @@
class bad_cast : public exception {
public:
// see \ref{exception} for the specification of the special member functions
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
};
}
\end{codeblock}
Expand All @@ -3326,7 +3327,7 @@

\indexlibrarymember{what}{bad_cast}%
\begin{itemdecl}
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -3344,7 +3345,7 @@
class bad_typeid : public exception {
public:
// see \ref{exception} for the specification of the special member functions
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
};
}
\end{codeblock}
Expand All @@ -3360,7 +3361,7 @@

\indexlibrarymember{what}{bad_typeid}%
\begin{itemdecl}
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -3775,16 +3776,16 @@
terminate_handler set_terminate(terminate_handler f) noexcept;
[[noreturn]] void terminate() noexcept;

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

using exception_ptr = @\unspec@;

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

Expand All @@ -3796,11 +3797,11 @@
namespace std {
class exception {
public:
exception() noexcept;
exception(const exception&) noexcept;
exception& operator=(const exception&) noexcept;
virtual ~exception();
virtual const char* what() const noexcept;
constexpr exception() noexcept;
constexpr exception(const exception&) noexcept;
constexpr exception& operator=(const exception&) noexcept;
constexpr virtual ~exception();
constexpr virtual const char* what() const noexcept;
};
}
\end{codeblock}
Expand Down Expand Up @@ -3833,8 +3834,8 @@
\indexlibraryctor{exception}%
\indexlibrarymember{operator=}{exception}%
\begin{itemdecl}
exception(const exception& rhs) noexcept;
exception& operator=(const exception& rhs) noexcept;
constexpr exception(const exception& rhs) noexcept;
constexpr exception& operator=(const exception& rhs) noexcept;
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -3846,7 +3847,7 @@

\indexlibrarydtor{exception}%
\begin{itemdecl}
virtual ~exception();
constexpr virtual ~exception();
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -3858,13 +3859,15 @@

\indexlibrarymember{what}{exception}%
\begin{itemdecl}
virtual const char* what() const noexcept;
constexpr virtual const char* what() const noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\returns
An \impldef{return value of \tcode{exception::what}} \ntbs{}.
An \impldef{return value of \tcode{exception::what}} \ntbs{},
which during constant evaluation is encoded with
the ordinary literal encoding\iref{lex.ccon}.

\pnum
\remarks
Expand All @@ -3885,7 +3888,7 @@
class bad_exception : public exception {
public:
// see \ref{exception} for the specification of the special member functions
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
};
}
\end{codeblock}
Expand All @@ -3900,7 +3903,7 @@

\indexlibrarymember{what}{bad_exception}%
\begin{itemdecl}
const char* what() const noexcept override;
constexpr const char* what() const noexcept override;
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -4007,7 +4010,7 @@

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

\begin{itemdescr}
Expand Down Expand Up @@ -4068,11 +4071,14 @@
Changes in the number of \tcode{exception_ptr} objects that refer to a
particular exception do not introduce a data race.
\end{note}

\pnum
All member functions are marked \tcode{constexpr}.
\end{itemdescr}

\indexlibraryglobal{current_exception}%
\begin{itemdecl}
exception_ptr current_exception() noexcept;
constexpr exception_ptr current_exception() noexcept;
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -4103,7 +4109,7 @@

\indexlibraryglobal{rethrow_exception}%
\begin{itemdecl}
[[noreturn]] void rethrow_exception(exception_ptr p);
[[noreturn]] constexpr void rethrow_exception(exception_ptr p);
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -4131,7 +4137,7 @@

\indexlibraryglobal{make_exception_ptr}%
\begin{itemdecl}
template<class E> exception_ptr make_exception_ptr(E e) noexcept;
template<class E> constexpr exception_ptr make_exception_ptr(E e) noexcept;
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -4160,18 +4166,18 @@
namespace std {
class nested_exception {
public:
nested_exception() noexcept;
nested_exception(const nested_exception&) noexcept = default;
nested_exception& operator=(const nested_exception&) noexcept = default;
virtual ~nested_exception() = default;
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;

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

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

Expand All @@ -4188,7 +4194,7 @@

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

\begin{itemdescr}
Expand All @@ -4199,7 +4205,7 @@

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

\begin{itemdescr}
Expand All @@ -4211,7 +4217,7 @@

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

\begin{itemdescr}
Expand All @@ -4222,7 +4228,7 @@

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

\begin{itemdescr}
Expand All @@ -4245,7 +4251,7 @@

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

\begin{itemdescr}
Expand Down
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