CWG2713 [dcl.init.aggr], [over.ics.list] should allow list-initialization of a reference-to-aggregate from a designated initializer list

[zygoloid]

Reference (section label): [dcl.init.list], [over.ics.list]

Link to reflector thread (if any): https://lists.isocpp.org/ext/2023/04/21015.php

Issue description:

[dcl.init.list] says that a designated-initializer-list can only be used to initialize an aggregate class. [over.ics.list] says that a designated-initializer-list can only be used to form an implicit conversion sequence for an aggregate. Longstanding implementation practice and expectations of consistency suggest that we should additionally permit initialization of a (const or rvalue) reference to aggregate class, creating a temporary as normal.

Suggested resolution:

Change in [dcl.init.list]/3.1:

• If the braced-init-list contains a designated-initializer-list and T is not a reference type, T shall be an aggregate class. [...]

Change in [over.ics.list]/2:

If the initializer list is a designated-initializer-list and the the parameter is not a reference, a conversion is only possible if the parameter has an aggregate type that can be initialized from the initializer list according to the rules for aggregate initialization ([dcl.init.aggr])

[jensmaurer]

CWG2713