P2927R3 Inspecting exception_ptr

Author: jensmaurer

source/support.tex

@@ -665,6 +665,7 @@
 #define @\defnlibxname{cpp_lib_erase_if}@                          202002L
   // also in \libheader{string}, \libheader{deque}, \libheader{forward_list}, \libheader{list}, \libheader{vector}, \libheader{map}, \libheader{set}, \libheader{unordered_map},
   // \libheader{unordered_set}
+#define @\defnlibxname{cpp_lib_exception_ptr_cast}@                202506L // also in \libheader{exception}
 #define @\defnlibxname{cpp_lib_exchange_function}@                 201304L // freestanding, also in \libheader{utility}
 #define @\defnlibxname{cpp_lib_execution}@                         201902L // also in \libheader{execution}
 #define @\defnlibxname{cpp_lib_expected}@                          202211L // also in \libheader{expected}
@@ -3864,6 +3865,8 @@
   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 E> 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);
@@ -4143,7 +4146,8 @@
 For purposes of determining the presence of a data race, operations on
 \tcode{exception_ptr} objects shall access and modify only the
 \tcode{exception_ptr} objects themselves and not the exceptions they refer to.
-Use of \tcode{rethrow_exception} on \tcode{exception_ptr} objects that refer to
+Use of \tcode{rethrow_exception} or \tcode{exception_ptr_cast}
+on \tcode{exception_ptr} objects that refer to
 the same exception object shall not introduce a data race.
 \begin{note}
 If
@@ -4240,6 +4244,32 @@
 \end{note}
 \end{itemdescr}
 
+\indexlibraryglobal{exception_ptr_cast}%
+\begin{itemdecl}
+template<class E> const E* exception_ptr_cast(const exception_ptr& p) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\mandates
+\tcode{E} is a cv-unqualified complete object type.
+\tcode{E} is not an array type.
+\tcode{E} is not a pointer or pointer-to-member type.
+\begin{note}
+When \tcode{E} is a pointer or pointer-to-member type,
+a handler of type \tcode{const E\&} can match
+without binding to the exception object itself.
+\end{note}
+
+\pnum
+\returns
+A pointer to the exception object referred to by \tcode{p},
+if \tcode{p} is not null and
+a handler of type \tcode{const E\&}
+would be a match\iref{except.handle} for that exception object.
+Otherwise, \tcode{nullptr}.
+\end{itemdescr}
+
 \rSec2[except.nested]{\tcode{nested_exception}}
 
 \indexlibraryglobal{nested_exception}%