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Add support for statement-as-expression #92

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Jul 23, 2023
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Add support for statement-as-expression #92

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43 changes: 39 additions & 4 deletions ltx/exprs.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,7 @@
\enumerator{Nullptr}
\enumerator{This}
\enumerator{TemplateReference}
\enumerator{Unused1}
\enumerator{Statement}
\enumerator{TypeTraitIntrinsic}
\enumerator{DesignatedInitializer}
\enumerator{PackedTemplateArguments}
Expand Down Expand Up @@ -1568,10 +1568,31 @@ \subsection{\valueTag{ExprSort::TemplateReference}}

\note{This structure is subject to removal in future releases.}

\subsection{\valueTag{ExprSort::Unused1}}
\label{sec:ifc:ExprSort:Unused1}
\subsection{\valueTag{ExprSort::Statement}}
\label{sec:ifc:ExprSort:Statement}

No structured is associated with this sort value.
A \type{ExprIndex} value with tag \valueTag{ExprSort::Statement} represents an abstract reference to a statement used
in a context where an expression would normally occur. Such a context could be in support of code transformation that
expands a function call to its body where arguments are substituted for parameters, or in support of some extensions
such as ``statement expressions''. Yet, another context would be to satisfy IFC-internal typing requirements
where a structure is notionally a statement, but needs to appear as argument to an operator expecting an expression
structure. In such cases, this structure effectively acts as an embedding of a statement structure in the
expression sort category. The \field{index} is an index into the statement-as-expression partition.
Each entry in that partition is a structure with the following layout
%
\begin{figure}[H]
\centering
\structure{
\DeclareMember{locus}{SourceLocation} \\
\DeclareMember{type}{TypeIndex} \\
\DeclareMember{stmt}{StmtIndex} \\
}
\end{figure}
%
and meanings for the fields
\begin{itemize}
\item \field{stmt} designates the statement being embedded in the expression sort category.
\end{itemize}


\subsection{\valueTag{ExprSort::TypeTraitIntrinsic}}
Expand Down Expand Up @@ -1892,6 +1913,9 @@ \subsection{Monadic operators}
\enumerator{MsvcConfusedPopState}
\enumerator{MsvcConfusedDtorAction}
\enumerator{MsvcConfusedVtorDisplacement}
\enumerator{MsvcConfusedDependentExpression}
\enumerator{MsvcConfusedSubstitution}
\enumerator{MsvcConfusedAggregateReturn}
\end{Enumeration}

\ifcSortSection{Unknown}{MonadicOperator}
Expand Down Expand Up @@ -2095,6 +2119,17 @@ \subsection{Monadic operators}
\ifcSortSection{MsvcConfusedDependentSizeof}{MonadicOperator}
Source-level \code{sizeof} operator, used in an expression where the operand is dependent.

\ifcSortSection{MsvcConfusedDependentExpression}{MonadicOperator}
This operator indicates a weakness in the current MSVC parser whereby certain expressions are explicitly
marked dependent (with no indication of whether they are type-dependent or value-dependent).

\ifcSortSection{MsvcConfusedSubstitution}{MonadicOperator}
This operator indicates a substitution of an expression (the operand) for a template parameter declaration
(the implementation field of the monadic tree).

\ifcSortSection{MsvcConfusedAggregateReturn}{MonadicOperator}
This operator indicates a semantic action of a \code{return} statement where the expression-to-return
evaluates to an aggregate with at least one subobject having non-trivial destructor.

\subsection{Dyadic operators}
\label{sec:ifc:OperatorSort:Dyadic}
Expand Down