This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

2272. Implicit initialization of aggregate members of reference type

[Adopted at the February/March, 2017 meeting.]

Consider:

  struct S {
    const int &i;
  } s{}; 

This example ought to be ill-formed, but 9.4.2 [dcl.init.aggr] paragraph 8 states that i is instead initialized from an empty initializer list, which causes i to bind to a value-initialized temporary of type int.

Proposed resolution (February, 2017):

1. Change 9.4.2 [dcl.init.aggr] paragraph 8 as follows:

If there are fewer initializer-clauses in the list than there are elements in the a non-union aggregate, then each element not explicitly initialized shall be initialized from its default member initializer (11.4 [class.mem]) or, if there is no default member initializer, from an empty initializer list (9.4.5 [dcl.init.list]). is initialized as follows:

• If the element has a default member initializer (11.4 [class.mem]), the element is initialized from that initializer.

• Otherwise, if the element is not a reference, the element is copy-initialized from an empty initializer list (9.4.5 [dcl.init.list]).

• Otherwise, the program is ill-formed.

If the aggregate is a union and the initializer list is empty, then

• if any variant member has a default member initializer, that member is initialized from its default member initializer;

• otherwise, the first member of the union (if any) is copy-initialized from an empty initializer list.

[Example:...

2. Delete 9.4.2 [dcl.init.aggr] paragraph 11:

If an incomplete or empty initializer-list leaves a member of reference type uninitialized, the program is ill-formed.

This resolution also resolves issues 1622 and 2116.