Skip to content

Commit

Permalink
do not try to normalize concept template parameter
Browse files Browse the repository at this point in the history
  • Loading branch information
@cor3ntin
cor3ntin committed Jun 26, 2024
1 parent aeee54d commit 8b44970
Showing 1 changed file with 131 additions and 107 deletions.
238 changes: 131 additions & 107 deletions src/D2841.tex
View file
Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,11 @@ \section{Abstract}

\section{Revisions}

\subsection{R4}

\begin{itemize}
\item Wording improvements
\end{itemize}

\subsection{R3}

Expand Down Expand Up @@ -2163,9 +2168,7 @@ \subsection{\textcolor{noteclr}{3. Wording for variable-template and concept tem
\begin{addedblock}

The associated constraints \tcode{C} of a declaration \tcode{D} are \emph{eligible for subsumption}
unless \tcode{D} is a templated declaration and \tcode{C} names a \grammarterm{concept-tt-parameter}.

% TODO: dependent does not mean anything
unless \tcode{C} contains an atomic constraint that names a \grammarterm{concept-tt-parameter}.

\end{addedblock}

Expand Down Expand Up @@ -2221,7 +2224,7 @@ \subsection{\textcolor{noteclr}{3. Wording for variable-template and concept tem
template <template <typename T> concept X, typename T>
int f(S<X, T>) requires X<T> { return 43; } // \#2

// error: the 3 following calls are ambiguous because \#1 and \#2 are not subsumption eligible
// error: the 3 following calls are ambiguous because \#1 and \#2 are not eligible for subsumption
// (their associated constraints depend on a concept template parameter X)
f(S<A, int>{});
f(S<C, int>{});
Expand Down Expand Up @@ -2261,21 +2264,18 @@ \subsection{\textcolor{noteclr}{3. Wording for variable-template and concept tem
\item
The normal form of a concept-id \tcode{C<A$_1$, A$_2$, ..., A$_n$>}
is the normal form of the \grammarterm{constraint-expression} of \tcode{C},
after \removed{substituting \tcode{A$_1$, A$_2$, ..., A$_n$}}
after substituting \tcode{A$_1$, A$_2$, ..., A$_n$} for
\begin{itemize}
\begin{addedblock}
\item substituting each use of A$_i$'s corresponding template parameter in the \grammarterm{constraint-expression} of \tcode{C} if A$_i$ denotes a \grammarterm{concept-name}
\item if A$_i$ names a \grammarterm{concept-name} \tcode{C2} and neither \tcode{C} nor \tcode{C2} names a concept template parameter, the \grammarterm{constraint-expression} of \tcode{C2} in \tcode{C};
\end{addedblock}
\item
\added{substituting each A$_i$ that is not a \grammarterm{concept-name}} for \tcode{C}{'s} respective template parameters in the
\added{otherwise, } \tcode{C}{'s} respective template parameters in the
parameter mappings in each atomic constraint.
\end{itemize}
If any such substitution results in an invalid type or expression,
the program is ill-formed; no diagnostic is required.

\end{itemize}

\ednote{We need wording to substitute C when C names a concept template parameter}

\begin{example}
\begin{codeblock}
template<typename T> concept A = T::value || true;
Expand All @@ -2295,118 +2295,142 @@ \subsection{\textcolor{noteclr}{3. Wording for variable-template and concept tem
in the parameter mapping.
\end{example}

\ednote{The wording in blue is added by P2963}
\begin{addedblockTwo}
\item For a \grammarterm{fold-operator} [expr.prim.fold] that is either \tcode{\&\&} or \tcode{||}
\end{addedblockTwo}
\begin{itemize}
\begin{addedblockTwo}
\item The normal form of an expression \tcode{( ... \grammarterm{fold-operator} E )} is the normal form of \tcode{( E \grammarterm{fold-operator}...)}.
\item The normal form of an expression \tcode{( E1 \grammarterm{fold-operator} ... \grammarterm{fold-operator} E2 )} is the the normal form of
\begin{itemize}
\item \tcode{(E1 \grammarterm{fold-operator}...) \grammarterm{fold-operator} E2} if \tcode{E1} contains an unexpanded pack, or
\item \tcode{E1 \grammarterm{fold-operator} (E2 \grammarterm{fold-operator}...)} otherwise.
\end{itemize}
\end{addedblockTwo}
\ednote{The wording in pink is added by P2963 and removed by this paper}
\begin{removedblockTwo}
\item The normal form of \tcode{(E \&\& ...)} is a fold expanded conjunction constraint \mbox{[temp.constr.fold]} whose constraint is the normal form of \tcode{E}.
\item The normal form of \tcode{(E || ...)} is a fold expanded disjunction constraint whose constraint is the normal form of \tcode{E}.
\end{removedblockTwo}

\ednote{Add the following two bullets}
\begin{addedblock}
\item If \tcode{E} contains an unexpanded pack \tcode{P} naming a concept-name, the normal form of \tcode{(E \grammarterm{fold-operator} ...)}
is the normal form of \tcode{(} \tcode{((}$\mathtt{E'}_0$ \placeholder{op} $\mathtt{E'}_1$\tcode{)} \placeholder{op} $\cdots$\tcode{)} \placeholder{op} $\mathtt{E'}_{N-1}$ \tcode{)} where $\mathtt{E'}_i$ is formed by substituting the $ith$ element of the corresponding template parameter of \tcode{P} in \tcode{E}.
\item Otherwise, the normal form of \tcode{(E \&\& ...)} is a fold expanded conjunction constraint \mbox{[temp.constr.fold]} whose constraint is the normal form of \tcode{E}
and the normal form of \tcode{(E || ...)} is a fold expanded disjunction constraint whose constraint is the normal form of \tcode{E}.
\begin{example}
\begin{codeblock}
template <typename T>
concept C = true;

template <template <typename T, template<typename...> concept> concept CT>
concept CC= CT<T>;

template <template <typename U, template<typename...> concept> concept CT>
void f() requires CT<U*, C>;

template <typename U>
void g() requires CC<U*, C>;
\end{codeblock}

The normal form of the associated constraints of \tcode{f} is the
atomic constraint \tcode{CT<T, C>} (with mapping $\tcode{T} \mapsto \tcode{U*}, ????$)

The normal form of the associated constraints of \tcode{g} is the
atomic constraint \tcode{true} (with mapping $\tcode{T} \mapsto \tcode{U*}$)
\end{example}
\end{addedblock}
\end{itemize}
%\begin{removedblockTwo}
%\item For a \grammarterm{fold-operator} [expr.prim.fold] that is either \tcode{\&\&} or \tcode{||},
%
%
%
%, the normal form of an expression \tcode{( ... \grammarterm{fold-operator} E )} is the normal form of \tcode{( E \grammarterm{fold-operator}...)}.
%\ednote{The wording in blue is added by P2963}
%\begin{addedblockTwo}
%\item For a \grammarterm{fold-operator} [expr.prim.fold] that is either \tcode{\&\&} or \tcode{||}
%\end{addedblockTwo}
%\begin{itemize}
%\begin{addedblockTwo}
%\item The normal form of an expression \tcode{( ... \grammarterm{fold-operator} E )} is the normal form of \tcode{( E \grammarterm{fold-operator}...)}.
%\item The normal form of an expression \tcode{( E1 \grammarterm{fold-operator} ... \grammarterm{fold-operator} E2 )} is the the normal form of
%\begin{itemize}
% \item \tcode{(E1 \grammarterm{fold-operator}...) \grammarterm{fold-operator} E2} if \tcode{E1} contains an unexpanded pack, or
% \item \tcode{E1 \grammarterm{fold-operator} (E2 \grammarterm{fold-operator}...)} otherwise.
%\end{itemize}
%\end{addedblockTwo}
%\ednote{The wording in pink is added by P2963 and removed by this paper}
%\begin{removedblockTwo}
%\item The normal form of \tcode{(E \&\& ...)} is a fold expanded conjunction constraint \mbox{[temp.constr.fold]} whose constraint is the normal form of \tcode{E}.
%\item The normal form of \tcode{(E || ...)} is a fold expanded disjunction constraint whose constraint is the normal form of \tcode{E}.
%\end{removedblockTwo}
%
%\ednote{Add the following two bullets}
%\begin{addedblock}
%\item If \tcode{E} contains an unexpanded pack \tcode{P} naming a concept-name, the normal form of \tcode{(E \grammarterm{fold-operator} ...)}
%is the normal form of \tcode{(} \tcode{((}$\mathtt{E'}_0$ \placeholder{op} $\mathtt{E'}_1$\tcode{)} \placeholder{op} $\cdots$\tcode{)} \placeholder{op} $\mathtt{E'}_{N-1}$ \tcode{)} where $\mathtt{E'}_i$ is formed by substituting the $ith$ element of the corresponding template parameter of \tcode{P} in \tcode{E}.
%\item Otherwise, the normal form of \tcode{(E \&\& ...)} is a fold expanded conjunction constraint \mbox{[temp.constr.fold]} whose constraint is the normal form of \tcode{E}
% and the normal form of \tcode{(E || ...)} is a fold expanded disjunction constraint whose constraint is the normal form of \tcode{E}.
%
%\item The normal form of a \grammarterm{fold-expression} \iref{expr.prim.fold} \tcode{F}
%whose \grammarterm{fold-operator} \tcode{op} is either \tcode{\&\&} or \tcode{||}
%and whose pattern is a \tcode{concept-name} \tcode{C} is the normal form of the expanded expression F'
%produced by the expansion of \tcode{C}:
%
%\pnum
%\begin{itemize}
% \item
% % Note: "\space" used below because " " inside tcode adds too much whitespace;
% % one could optionally use mathfont inside tcode, e.g., "\tcode{($ $}".
% \tcode{(}\space
% \tcode{((}$\mathtt{E}_1$
% \placeholder{op} $\mathtt{E}_2$\tcode{)}
% \placeholder{op} $\cdots$\tcode{)}
% \placeholder{op} $\mathtt{E}_N$
% \space\tcode{)}
% for a unary left fold,
% \item
% \tcode{(}\space
% $\mathtt{E}_1$ \placeholder{op}
% \tcode{(}$\cdots$ \placeholder{op}
% \tcode{(}$\mathtt{E}_{N-1}$ \placeholder{op}
% $\mathtt{E}_N$\tcode{))}
% \space\tcode{)}
% for a unary right fold,
% \item
% \tcode{(}\space
% \tcode{(((}$\mathtt{E}$
% \placeholder{op} $\mathtt{E}_1$\tcode{)}
% \placeholder{op} $\mathtt{E}_2$\tcode{)}
% \placeholder{op} $\cdots$\tcode{)}
% \placeholder{op} $\mathtt{E}_N$
% \space\tcode{)}
% for a binary left fold, and
% \item
% \tcode{(}\space
% $\mathtt{E}_1$ \placeholder{op}
% \tcode{(}$\cdots$ \placeholder{op}
% \tcode{(}$\mathtt{E}_{N-1}$ \placeholder{op}
% \tcode{(}$\mathtt{E}_{N}$ \placeholder{op}
% $\mathtt{E}$\tcode{)))}
% \space\tcode{)}
% for a binary right fold.
%\end{itemize}
%\end{addedblock}


\item
The normal form of any other expression \tcode{E} is
the atomic constraint
whose expression is \tcode{E} and
whose parameter mapping is the identity mapping.
%\end{itemize}
%%\begin{removedblockTwo}
%%\item For a \grammarterm{fold-operator} [expr.prim.fold] that is either \tcode{\&\&} or \tcode{||},
%%
%%
%%
%%, the normal form of an expression \tcode{( ... \grammarterm{fold-operator} E )} is the normal form of \tcode{( E \grammarterm{fold-operator}...)}.
%%\item The normal form of an expression \tcode{( E1 \grammarterm{fold-operator} ... \grammarterm{fold-operator} E2 )} is the the normal form of
%%\begin{itemize}
%% \item \tcode{(E1 \grammarterm{fold-operator}...) \grammarterm{fold-operator} E2} if \tcode{E1} contains an unexpanded pack, or
%% \item \tcode{E1 \grammarterm{fold-operator} (E2 \grammarterm{fold-operator}...)} otherwise.
%%\end{itemize}
%%\item The normal form of \tcode{(E \&\& ...)} is a fold expanded conjunction constraint \mbox{[temp.constr.fold]} whose constraint is the normal form of \tcode{E}.
%%\item The normal form of \tcode{(E || ...)} is a fold expanded disjunction constraint whose constraint is the normal form of \tcode{E}.
%%\end{removedblockTwo}
%%
%%
%%\item The normal form of a \grammarterm{fold-expression} \iref{expr.prim.fold} \tcode{F}
%%whose \grammarterm{fold-operator} \tcode{op} is either \tcode{\&\&} or \tcode{||}
%%and whose pattern is a \tcode{concept-name} \tcode{C} is the normal form of the expanded expression F'
%%produced by the expansion of \tcode{C}:
%%
%%\pnum
%%\begin{itemize}
%% \item
%% % Note: "\space" used below because " " inside tcode adds too much whitespace;
%% % one could optionally use mathfont inside tcode, e.g., "\tcode{($ $}".
%% \tcode{(}\space
%% \tcode{((}$\mathtt{E}_1$
%% \placeholder{op} $\mathtt{E}_2$\tcode{)}
%% \placeholder{op} $\cdots$\tcode{)}
%% \placeholder{op} $\mathtt{E}_N$
%% \space\tcode{)}
%% for a unary left fold,
%% \item
%% \tcode{(}\space
%% $\mathtt{E}_1$ \placeholder{op}
%% \tcode{(}$\cdots$ \placeholder{op}
%% \tcode{(}$\mathtt{E}_{N-1}$ \placeholder{op}
%% $\mathtt{E}_N$\tcode{))}
%% \space\tcode{)}
%% for a unary right fold,
%% \item
%% \tcode{(}\space
%% \tcode{(((}$\mathtt{E}$
%% \placeholder{op} $\mathtt{E}_1$\tcode{)}
%% \placeholder{op} $\mathtt{E}_2$\tcode{)}
%% \placeholder{op} $\cdots$\tcode{)}
%% \placeholder{op} $\mathtt{E}_N$
%% \space\tcode{)}
%% for a binary left fold, and
%% \item
%% \tcode{(}\space
%% $\mathtt{E}_1$ \placeholder{op}
%% \tcode{(}$\cdots$ \placeholder{op}
%% \tcode{(}$\mathtt{E}_{N-1}$ \placeholder{op}
%% \tcode{(}$\mathtt{E}_{N}$ \placeholder{op}
%% $\mathtt{E}$\tcode{)))}
%% \space\tcode{)}
%% for a binary right fold.
%%\end{itemize}
%%\end{addedblock}
%
%
%\item
%The normal form of any other expression \tcode{E} is
%the atomic constraint
%whose expression is \tcode{E} and
%whose parameter mapping is the identity mapping.
\end{itemize}

\pnum
The process of obtaining the normal form of a
\grammarterm{constraint-expression}
is called
\defnx{normalization}{normalization!constraint|see{constraint, normalization}}.
\begin{note}
Normalization of \grammarterm{constraint-expression}{s}
is performed
when determining the associated constraints \iref{temp.constr.constr}
of a declaration
and
when evaluating the value of an \grammarterm{id-expression}
that names a concept specialization \iref{expr.prim.id}.
\end{note}
%
%\pnum
%The process of obtaining the normal form of a
%\grammarterm{constraint-expression}
%is called
%\defnx{normalization}{normalization!constraint|see{constraint, normalization}}.
%\begin{note}
% Normalization of \grammarterm{constraint-expression}{s}
% is performed
% when determining the associated constraints \iref{temp.constr.constr}
% of a declaration
% and
% when evaluating the value of an \grammarterm{id-expression}
% that names a concept specialization \iref{expr.prim.id}.
%\end{note}

\rSec2[temp.variadic]{Variadic templates}

Expand Down

0 comments on commit 8b44970

Please sign in to comment.