[Voted into WP at March, 2010 meeting.]

Proposed resolution (October, 2009):

Change 11.4.5 [class.ctor] paragraph 5, the second list, as follows:

An implicitly-declared default constructor for class X is defined as deleted if:

• X is a union-like class that has a variant member with a non-trivial default constructor,

• any non-static data member with no brace-or-equal-initializer is of reference type,

• any non-static data member of const-qualified type (or array thereof) with no brace-or-equal-initializer does not have a user-provided default constructor, or

• any direct or virtual base class, or non-static data member with no brace-or-qual-initializer, or direct or virtual base class has class type M (or array thereof) and either M has no default constructor, or if constructor or overload resolution (12.2 [over.match]) as applied to M's default constructor, results in an ambiguity or in a function that is deleted or inaccessible from the implicitly-declared default constructor.

The reasons for which an implicitly-declared default constructor is defined as deleted, given in 11.4.5 [class.ctor] paragraph 4, all deal with cases in which a member cannot be default-initialized. Presumably a brace-or-equal-initializer for such a member would eliminate the need to define the constructor as deleted, but this case is not addressed by the current wording.