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

594. Coordinating issues 119 and 404 with delegating constructors

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

In ISO/IEC 14882:2003, the second bullet of 6.7.4 [basic.life] paragraph 1 reads,

if T is a class type with a non-trivial constructor (11.4.5 [class.ctor]), the constructor call has completed.

Issue 119 pointed out that aggregate initialization can be used with some classes with a non-trivial implicitly-declared default constructor, and that in such cases there is no call to the object's constructor. The resolution for that issue was to change the previously-cited wording to read,

If T is a class type with a non-trivial constructor (11.4.5 [class.ctor], the initialization is complete.

Later (but before the WP was revised with the wording from the resolution of issue 119), issue 404 changed the 2003 wording to read,

If T is a class type and the constructor invoked to create the object is non-trivial (11.4.5 [class.ctor]), the constructor call has completed.

thus reversing the effect of issue 119, whose whole purpose was to cover objects with non-trivial constructors that are not invoked.

Through an editorial error, the post-Redmond draft (N1905) still contained the original 2003 wording that should have been replaced by the resolution of issue 119, in addition to the new wording from the resolution:

if T is a class type and the constructor invoked to create the object is non-trivial (11.4.5 [class.ctor]), the constructor call has completed. the initialization is complete.

Finally, during the application of the edits for delegating constructors (N1986), this editing error was “fixed” by retaining the original 2003 wording (which was needed for the application of the change specified in N1986), so that the current draft (N2009) reads,

if T is a class type and the constructor invoked to create the object is non-trivial (11.4.5 [class.ctor]), the principal constructor call 11.9.3 [class.base.init]) has completed.

Because the completion of the call to the principal constructor corresponds to the point at which the object is “fully constructed” (14.3 [except.ctor] paragraph 2), i.e., its initialization is complete, I believe that the exact wording of the issue 119 resolution would be correct and should be restored verbatim.

Proposed resolution (June, 2008):

Change 6.7.4 [basic.life] paragraph 1 as follows:

The lifetime of an object is a runtime property of the object. An object is said to have non-trivial initialization if it is of a class or aggregate type and it or one of its members is initialized by a constructor other than a trivial default constructor. [Note: Initialization by a trivial copy constructor is non-trivial initialization. —end note] The lifetime of an object of type T begins when:

• storage with the proper alignment and size for type T is obtained, and

• if T is a class type and the constructor invoked to create the object is non-trivial (11.4.5 [class.ctor]), the principal constructor call (11.9.3 [class.base.init]) has completed. [Note: the initialization can be performed by a constructor call or, in the case of an aggregate with an implicitly-declared non-trivial default constructor, an aggregate initialization 9.4.2 [dcl.init.aggr]. —end note] the object has non-trivial initialization, its initialization is complete.

The lifetime of an object of type T ends when...