This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

644. Should a trivial class type be a literal type?

[Voted into the WP at the June, 2008 meeting.]

The original proposed wording for 6.8 [basic.types] paragraph 11 required a constexpr constructor for a literal class only “if the class has at least one user-declared constructor.” This wording was dropped during the review by CWG out of a desire to ensure that literal types not have any uninitialized members. Thus, a class like

    struct pixel {
        int x, y;
    };

is not a literal type. However, if an object of that type is aggregate-initialized or value-initialized, there can be no uninitialized members; the missing wording should be restored in order to permit use of expressions like pixel().x as constant expressions.

Proposed resolution (February, 2008):

Change 6.8 [basic.types] paragraph 10 as follows:

A type is a literal type if it is:

• a scalar type; or
• a class type (Clause 11 [class]) with
• a trivial copy constructor,
• a trivial destructor,
• a trivial default constructor or at least one constexpr constructor other than the copy constructor,
• no virtual base classes, and
• all non-static data members and base classes of literal types; or
• an array of literal type.