P3450R1 Extend std::is_within_lifetime

Fixes NB US 82-145 (C++26 CD).

Author: eisenwave

source/meta.tex

@@ -647,7 +647,8 @@
 
   // \ref{meta.const.eval}, constant evaluation context
   constexpr bool is_constant_evaluated() noexcept;
-  consteval bool is_within_lifetime(const auto*) noexcept;
+  template<class U=void, class T>
+    consteval bool is_within_lifetime(const T*) noexcept;
 }
 \end{codeblock}
 
@@ -2844,14 +2845,21 @@
 
 \indexlibraryglobal{is_within_lifetime}%
 \begin{itemdecl}
-consteval bool is_within_lifetime(const auto* p) noexcept;
+template<class U=void, class T>
+    consteval bool is_within_lifetime(const T* p) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+\mandates
+\tcode{static_cast<const volatile U*>(p)} is well-formed.
+
 \pnum
 \returns
 \tcode{true} if \tcode{p} is a pointer to an object that is
-within its lifetime\iref{basic.life}; otherwise, \tcode{false}.
+within its lifetime\iref{basic.life} and
+\tcode{static_cast<const volatile U*>(p)} is a constant subexpression;
+otherwise, \tcode{false}.
 
 \pnum
 \remarks

source/support.tex

@@ -749,7 +749,7 @@
 #define @\defnlibxname{cpp_lib_is_sufficiently_aligned}@           202411L // freestanding, also in \libheader{memory}
 #define @\defnlibxname{cpp_lib_is_swappable}@                      201603L // freestanding, also in \libheader{type_traits}
 #define @\defnlibxname{cpp_lib_is_virtual_base_of}@                202406L // freestanding, also in \libheader{type_traits}
-#define @\defnlibxname{cpp_lib_is_within_lifetime}@                202306L // freestanding, also in \libheader{type_traits}
+#define @\defnlibxname{cpp_lib_is_within_lifetime}@                202603L // freestanding, also in \libheader{type_traits}
 #define @\defnlibxname{cpp_lib_jthread}@                           201911L // also in \libheader{stop_token}, \libheader{thread}
 #define @\defnlibxname{cpp_lib_latch}@                             201907L // also in \libheader{latch}
 #define @\defnlibxname{cpp_lib_launder}@                           201606L // freestanding, also in \libheader{new}