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

2025-09-28

3041. Overly aggressive rule for deleting the destructor of a union

(From submission #722.)

Paper P3074R7 added an overly aggressive rule to delete destructors of unions, making the following example have a deleted destructor:

  union U {
    U(int i) : i(i) { }
    int i;
  };

Suggested resolution:

Change in 11.4.7 [class.dtor] paragraph 7 as follows:

A defaulted destructor for a class X is defined as deleted if

• X is a non-union class and any non-variant potentially constructed subobject has class type M (or possibly multidimensional array thereof) where M has a destructor that is deleted or is inaccessible from the defaulted destructor,
• X is a union and there is a subobject S of class type M (or possibly multi-dimensional array thereof) where M has a destructor that is deleted, inaccessible from the defaulted destructor, or non-trivial, and either
  • overload resolution to select a constructor to default-initialize an object of type X either fails or selects a constructor that is either deleted or not trivial user-provided, or
  • X has a variant member V of class type M (or possibly multi-dimensional array thereof) where V S has a default member initializer and M has a destructor that is non-trivial, or,
• for a virtual destructor, lookup of the non-array deallocation function results in an ambiguity or in a function that is deleted or inaccessible from the defaulted destructor.