Title
List-initialization of references
Status
cd2
Section
9.4.5 [dcl.init.list]
Submitter
Mike Miller

Created on 2009-07-08.00:00:00 last changed 143 months ago

Messages

Date: 2009-10-15.00:00:00

[Voted into WP at October, 2009 meeting.]

Date: 2009-07-15.00:00:00

Proposed resolution (July, 2009):

  1. Move the third bullet of the list in 9.4 [dcl.init] paragraph 16 to the top of the list:

    • If the initializer is a braced-init-list, the object is list-initialized (9.4.5 [dcl.init.list]).

    • If the destination type is a reference type, see 9.4.4 [dcl.init.ref].

    • ...

  2. Change 9.4.5 [dcl.init.list] paragraph 3, bullets 4 and 5, as follows:

    • Otherwise, if T is a reference to class type, or if T is any reference type and the initializer list has no elements, an rvalue temporary of the type referenced by T is list-initialized, and the reference is bound to that temporary. [Note:...

    • Otherwise (i.e., if T is not an aggregate, class type, or reference), if the initializer list has a single element...

Date: 2009-07-08.00:00:00

According to 9.4.5 [dcl.init.list] paragraph 3,

Otherwise, if T is a reference type, an rvalue temporary of the type referenced by T is list-initialized, and the reference is bound to that temporary.

This means, for an example like

    int i;
    const int& r1{ i };
    int&& r2{ i };

r1 is bound to a temporary containing the value of i, not to i itself, which seems surprising. Also, there's no prohibition here against binding the rvalue reference to an lvalue, as there is in 9.4.4 [dcl.init.ref] paragraph 5 bullet 2, so the initialization of r2 is well-formed, even though the corresponding non-list initialization int&& r3(i) is ill-formed.

There's also a question as to whether this bullet even applies to these examples. According to the decision tree in 9.4 [dcl.init] paragraph 16, initialization of a reference is dispatched to 9.4.4 [dcl.init.ref] in the first bullet, so these cases never make it to the third bullet sending the remaining braced-init-list cases to 9.4.5 [dcl.init.list]. If that's the correct interpretation, there's a problem with 9.4.4 [dcl.init.ref], since it doesn't deal with the braced-init-list cases, and the bullet in 9.4.5 [dcl.init.list] paragraph 3 dealing with references is dead code that's never used.

History
Date User Action Args
2010-03-29 00:00:00adminsetstatus: dr -> cd2
2009-11-08 00:00:00adminsetmessages: + msg2464
2009-11-08 00:00:00adminsetstatus: ready -> dr
2009-08-03 00:00:00adminsetmessages: + msg2169
2009-07-08 00:00:00admincreate