[2026-06 CWG Motion 12] P3847R1 Lexical order for lambdas

source/expressions.tex

@@ -2986,11 +2986,10 @@
 \tcode{\&} \opt{\tcode{...}} \grammarterm{identifier} \grammarterm{initializer}.
 \end{itemize}
 For each entity captured by copy, an
-unnamed non-static data member is declared in the closure type. The declaration order of
-these members is unspecified. The type of such a data member is
-the referenced type if the entity is a reference to an object,
-an lvalue reference to the referenced function type if the entity is a reference to a function, or
-the type of the corresponding captured entity otherwise.
+unnamed non-static data member is declared in the closure type.
+The type of such a data member is the referenced type if the entity is a reference to an object,
+an lvalue reference to the referenced function type if the entity is a reference to a function,
+or the type of the corresponding captured entity otherwise.
 A member of an anonymous union shall not be captured by copy.
 
 \pnum
@@ -3091,18 +3090,34 @@
 \end{codeblock}
 \end{example}
 
+\pnum
+The non-static data members in the closure type are declared in an unspecified order,
+except that the members introduced for explicit captures are declared in an order
+consistent with that of those captures.
+
 \pnum
 The entities that are
 captured by copy are used to direct-initialize each corresponding non-static data member
-of the resulting closure object, and the non-static data members corresponding to the
-\grammarterm{init-capture}{s} are initialized as indicated by the corresponding
-\grammarterm{initializer} (which may be copy- or direct-initialization). (For array members, the array elements are
-direct-initialized in increasing subscript order.) These initializations are performed
-when the \grammarterm{lambda-expression} is evaluated and
-in the (unspecified) order in which the non-static data members are declared.
+of the resulting closure object. The non-static data members corresponding to the
+\grammarterm{init-capture}{s} and the (reference) variables declared by \grammarterm{init-capture}{s}
+without corresponding non-static data members are initialized as indicated by the corresponding
+\grammarterm{initializer} (which may be copy- or direct-initialization).
+(For array members, the array elements are direct-initialized in increasing subscript order.)
+These initializations are performed when the \grammarterm{lambda-expression} is evaluated,
+in an order consistent with the (unspecified) order in which the non-static data members are declared
+and with the order of explicit captures.
 \begin{note}
 This ensures that the destructions will occur in the reverse order of the constructions.
 \end{note}
+\begin{example}
+\begin{codeblock}
+void f(std::vector<int> &&v) {
+  [size = v.size(),
+   own = std::move(v)] {};
+}
+\end{codeblock}
+Since \tcode{size} is initialized before \tcode{own}, it contains the original size of \tcode{v}.
+\end{example}
 
 \pnum
 \begin{note}