This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 118c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-10-24

3089. const-default-constructible improperly handles std::meta::info

A class that contains only std::meta::info data members, or arrays thereof, should be const-default-constructible.

Proposed resolution (approved by CWG 2025-10-24):

Change in 9.5.1 [dcl.init.general] paragraph 8 as follows (add bullets):

A class type cv T is const-default-constructible if

• T is std::meta::info;
• T is std::nullptr_t;
• default-initialization of T would invoke a user-provided constructor of T (not inherited from a base class);
• or if T is a class type where
  • each direct non-variant non-static data member M of T has a default member initializer or, if M is of class type X (or array thereof), X is const-default-constructible type,
  • if T is a union with at least one non-static data member, exactly one variant member has a default member initializer,
  • if T is not a union, for the type of each anonymous union member is const-default-constructible with at least one non-static data member (if any), exactly one non-static data member has a default member initializer, and
  • each potentially constructed base class of T is const-default-constructible.; or
• T is an array of const-default-constructible type.

If a program calls for the default-initialization of an object of a const-qualified type T, T shall be std::meta::info or a const-default-constructible class type, or array thereof.