Proposed resolution (approved by CWG 2022-08-26):

Insert before 9.5.1 [dcl.init.general] paragraph 18 as follows:

An initializer-clause followed by an ellipsis is a pack expansion (13.7.4 [temp.variadic]).

Initialization includes the evaluation of all subexpressions of each initializer-clause of the initializer (possibly nested within braced-init-lists) and the creation of any temporary objects for function arguments or return values (6.7.7 [class.temporary]).

If the initializer is a parenthesized expression-list, the expressions are evaluated in the order specified for function calls (7.6.1.3 [expr.call]).

Suggested resolution [SUPERSEDED]:

Insert before 9.5.1 [dcl.init.general] paragraph 18 as follows:

An initializer-clause followed by an ellipsis is a pack expansion (13.7.4 [temp.variadic]).

Initialization includes the evaluation of all subexpressions of each initializer-clause of the initializer (possibly nested within braced-init-lists).

If the initializer is a parenthesized expression-list, the expressions are evaluated in the order specified for function calls (7.6.1.3 [expr.call]).

[Accepted as a DR at the November, 2022 meeting.]

Subclause 7.6.1.3 [expr.call] paragraph 8 specifies:

The postfix-expression is sequenced before each expression in the expression-list and any default argument. The initialization of a parameter, including every associated value computation and side effect, is indeterminately sequenced with respect to that of any other parameter. [Note 8: All side effects of argument evaluations are sequenced before the function is entered (see 6.9.1 [intro.execution]). —end note]

Consider:

  f(std::unique_ptr<int>(new int),std::unique_ptr<int>(new int));

It is not clear from the phrasing whether the evaluation of each new int is part of the "initialization of [its] parameter" or whether only the initialization of f's parameters from the completed std::unique_ptr<int> objects is included. The note does not help, since it can be read as distinguishing argument evaluations from initialization.