P2996R13 Reflection for C++26

Author: Eisenwave

source/compatibility.tex

@@ -13,6 +13,22 @@
 
 \rSec2[diff.cpp23.lex]{\ref{lex}: Lexical conventions}
 
+\diffref{lex.operators}
+\change
+New operator \tcode{\caret\caret}.
+\rationale
+Required for new features.
+\effect
+Valid \CppXXIII{} that contains two consecutive \tcode{\caret} tokens
+can be ill-formed in this revision of \Cpp{}.
+\begin{example}
+\begin{codeblock}
+struct C { int operator^(int); };
+int operator^(int (C::*p)(int), C);
+int i = &C::operator^^C{};      // ill-formed; previously well-formed
+\end{codeblock}
+\end{example}
+
 \diffref{lex.key}
 \change
 New keywords.
@@ -148,6 +164,23 @@
 \end{codeblock}
 \end{example}
 
+\diffref{dcl.attr.grammar}
+\change
+New token \tcode{:]}.
+\rationale
+Required for new features.
+\effect
+Valid \CppXXIII{} that contained an \grammarterm{attribute-specifier}
+with an \grammarterm{attribute-using-prefix}
+but no attributes and no whitespace
+is ill-formed in this revision of \Cpp{}.
+\begin{example}
+\begin{codeblock}
+struct [[using CC:]] C;         // ill-formed; previously well-formed
+struct [[using DD: ]] D;        // OK
+\end{codeblock}
+\end{example}
+
 \rSec2[diff.cpp23.temp]{\ref{temp}: templates}
 
 \diffref{temp.constr}
@@ -221,6 +254,8 @@
 \libheaderref{hive},
 \libheaderrefx{inplace_vector}{inplace.vector.syn},
 \libheaderref{linalg},
+%FIXME: \libheaderref{meta} after renaming to meta.syn
+\libheaderrefx{meta}{meta.type.synop},
 \libheaderref{rcu},
 \libheaderref{simd},
 \libheaderref{stdbit.h},

source/lib-intro.tex

@@ -368,6 +368,11 @@
 and also define the function as deleted.
 \end{example}
 
+\item
+\constantwhen
+the conditions that are required for a call to the function
+to be a constant subexpression\iref{defns.const.subexpr}.
+
 \item
 \expects
 conditions that the function assumes to hold whenever it is called;
@@ -454,6 +459,7 @@
 Next, the semantics of the code sequence are determined by the
 \Fundescx{Constraints},
 \Fundescx{Mandates},
+\Fundescx{Constant When},
 \Fundescx{Preconditions},
 \Fundescx{Hardened preconditions},
 \Fundescx{Effects},
@@ -1223,8 +1229,8 @@
 \tcode{<flat_map>} \\
 \tcode{<flat_set>} \\
 \tcode{<format>} \\
-\tcode{<forward_list>} \\
 \columnbreak
+\tcode{<forward_list>} \\
 \tcode{<fstream>} \\
 \tcode{<functional>} \\
 \tcode{<future>} \\
@@ -1248,8 +1254,9 @@
 \tcode{<mdspan>} \\
 \tcode{<memory>} \\
 \tcode{<memory_resource>} \\
-\tcode{<mutex>} \\
 \columnbreak
+\tcode{<meta>} \\
+\tcode{<mutex>} \\
 \tcode{<new>} \\
 \tcode{<numbers>} \\
 \tcode{<numeric>} \\
@@ -1271,9 +1278,9 @@
 \tcode{<span>} \\
 \tcode{<spanstream>} \\
 \tcode{<sstream>} \\
+\columnbreak
 \tcode{<stack>} \\
 \tcode{<stacktrace>} \\
-\columnbreak
 \tcode{<stdexcept>} \\
 \tcode{<stdfloat>} \\
 \tcode{<stop_token>} \\
@@ -3082,6 +3089,26 @@
 either a standard library non-static member function\iref{member.functions}
 or an instantiation of a standard library member function template.
 
+\pnum
+Let \tcode{\placeholder{F}} denote
+a standard library function or function template.
+Unless \tcode{\placeholder{F}} is designated an addressable function,
+it is unspecified if or how
+a reflection value designating the associated entity can be formed.
+%FIXME: Why is this not an example, but a note that begins with "For example"?
+\begin{note}
+For example, it is possible that \tcode{std::meta::members_of}
+will not return reflections of standard library functions
+that an implementation handles through an extra-linguistic mechanism.
+\end{note}
+
+\pnum
+Let \tcode{\placeholder{F}} denote
+a standard library class or class template specialization.
+It is unspecified if or how
+a reflection value can be formed to any private member of \tcode{\placeholder{F}},
+or what the names of such members may be.
+
 \pnum
 A translation unit shall not declare namespace \tcode{std} to be an inline namespace\iref{namespace.def}.
 

source/macros.tex

@@ -363,6 +363,7 @@
 \newcommand{\required}{\Fundesc{Required behavior}}
 \newcommand{\constraints}{\Fundesc{Constraints}}
 \newcommand{\mandates}{\Fundesc{Mandates}}
+\newcommand{\constantwhen}{\Fundesc{Constant When}}
 \newcommand{\expects}{\Fundesc{Preconditions}}
 \newcommand{\hardexpects}{\Fundesc{Hardened preconditions}}
 \newcommand{\effects}{\Fundesc{Effects}}
@@ -465,6 +466,10 @@
 \newcommand{\unspecuniqtype}{\UNSP{unspecified unique type}}
 \newcommand{\unspecalloctype}{\UNSP{unspecified allocator type}}
 
+%% Convenience macro for double carets in expressions,
+%% particularly within \tcode.
+\newcommand{\reflexpr}[1]{\caret\caret#1}
+
 %% Manual insertion of italic corrections, for aligning in the presence
 %% of the above annotations.
 \newlength{\itcorrwidth}