This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2023-01-15


2598. Unions should not require a non-static data member of literal type

Section: 6.8.1  [basic.types.general]     Status: DR     Submitter: Richard Smith     Date: 2022-06-18

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

According to 6.8.1 [basic.types.general] paragraph 10, a type is a literal type only if it satisfies the following:

A type is a literal type if it is: [Note 4: A literal type is one for which it might be possible to create an object within a constant expression. ... —end note]

However, the normative rule disagrees with the note. Consider:

  struct A { A(); };
  union U {
    A a;
    constexpr U() {}
    constexpr ~U() {}
  };

It is certainly possible to create an object of type U in a constant expression, even though U is not a literal type.

In the suggested resolution, the aggregate type rule is intended to capture the fact that it is not possible for aggregate initialization of a non-empty union to leave no active member (and similarly for each anonymous union member in a non-union union-like class).

Suggested resolution [SUPERSEDED]:

Change in 6.8.1 [basic.types.general] paragraph 10 as follows:

A type is a literal type if it is:

Proposed resolution (CWG telecon 2022-08-12) [SUPERSEDED]:

Change in 6.8.1 [basic.types.general] paragraph 10 as follows:

A type is a literal type if it is:

Proposed resolution (approved by CWG 2022-11-09):

Change 6.8.1 [basic.types.general] paragraph 10 as follows:

A type is a literal type if it is: