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

655. Initialization not specified for forwarding constructors

[Voted into WP at August, 2010 meeting.]

The changes for delegating constructors overlooked the need to change 11.9.3 [class.base.init] paragraph 3:

The expression-list in a mem-initializer is used to initialize the base class or non-static data member subobject denoted by the mem-initializer-id. The semantics of a mem-initializer are as follows:

• if the expression-list of the mem-initializer is omitted, the base class or member subobject is value-initialized (see 9.4 [dcl.init]);

• otherwise, the subobject indicated by mem-initializer-id is direct-initialized using expression-list as the initializer (see 9.4 [dcl.init]).

The initialization of each base and member constitutes a full-expression. Any expression in a mem-initializer is evaluated as part of the full-expression that performs the initialization.

This paragraph deals only with subobjects; it needs to be made more general to apply to the complete object as well when the mem-initializer-id designates the constructor's class.

Proposed resolution (June, 2008):

Change 11.9.3 [class.base.init] paragraph 3 as follows:

The expression-list in a mem-initializer is used to initialize the base class or non-static data member subobject denoted by the mem-initializer-id. The semantics of a mem-initializer are A mem-initializer in which the mem-initializer-id names the constructor's class initializes the object by invoking the selected target constructor with the mem-initializer's expression-list. A mem-initializer in which the mem-initializer-id names a base class or non-static data member initializes the designated subobject as follows:

• if the expression-list of the mem-initializer is omitted, the base class or member subobject is value-initialized (see 9.4 [dcl.init]);

• otherwise, the subobject indicated by mem-initializer-id is direct-initialized using expression-list as the initializer (see 9.4 [dcl.init]).

...

The initialization of each base and member performed by each mem-initializer constitutes a full-expression. Any expression...

Notes from the September, 2008 meeting:

This text was significantly modified by N2756 (nonstatic data member initializers) and needs to be reworked in light of those changes.

Proposed resolution (February, 2010):

1. Change 11.9.3 [class.base.init] paragraph 7 as follows:

The expression-list or braced-init-list in a mem-initializer is used to initialize the base class or non-static data member subobject denoted by the mem-initializer-id designated subobject (or, in the case of a delegating constructor, the complete class object) according to the initialization rules of 9.4 [dcl.init] for direct-initialization.

[Example: ...

—end example] The initialization of each base and member performed by each mem-initializer constitutes a full-expression...

2. Change 11.9.3 [class.base.init] paragraph 8 as follows:

If In a non-delegating constructor, if a given non-static data member or base class is not named by a mem-initializer-id...

3. Change 11.9.3 [class.base.init] paragraph 10 as follows:

Initialization In a non-delegating constructor, initialization proceeds in the following order:

4. Change 11.9.3 [class.base.init] paragraph 12 as follows (this is an unrelated change correcting an error noticed while preparing the resolution of this issue):

Names in the expression-list or braced-init-list of a mem-initializer are evaluated in the scope of the constructor...

5. Change the next-to-last bullet of the note in 9.4.5 [dcl.init.list] paragraph 1 as follows:

• as a base-or-member initializer in a mem-initializer (11.9.3 [class.base.init])