Movatterモバイル変換

[Moved to DR at the April, 2013 meeting.]

Proposed resolution (February, 2012):

Move 12.2.4.3 [over.ics.rank] paragraph 3, first bullet, thirdsub-bullet, after the current fifth sub-bullet, as follows:

Two implicit conversion sequences of the same form areindistinguishable conversion sequences unless one of the followingrules applies:

• Standard conversion sequenceS1 is a betterconversion sequence...

• S1 is a proper subsequence ofS2...

• the rank ofS1 is better...

• S1 andS2 differ only in theirqualification conversion... —end example] or if notthat,

• S1 andS2 are reference bindings(9.5.4 [dcl.init.ref]) and neither refers... or if notthat,

• S1 andS2 are reference bindings(9.5.4 [dcl.init.ref]) and S1 binds... —endexample]or if not that,

• S1 andS2 differ only in theirqualification conversion... —end example]or if not that,

• S1 andS2 are reference bindings(9.5.4 [dcl.init.ref]), and the types to which the referencesrefer...

• User-defined conversion sequenceU1...

Notes from the February, 2012 meeting:

The CWG agreed that bullets 3 and 4 should be reversed, to checkthe reference binding first and then for qualification conversion.

The rule in 12.2.4.3 [over.ics.rank] paragraph 3 for rankingbased on a difference in qualification conversion applies only if they"differ only in their qualification conversion".

It is unclear as to whether the property of being a referencebinding is a factor in determining if there is a differencebetween conversion sequences. Notice that 12.2.4.2.5 [over.ics.ref] maps reference bindings to other forms ofimplicit conversion sequences, but does not state that theproperty of being a reference binding is preserved; however,12.2.4.3 [over.ics.rank] has cases which depend on whethercertain standard conversion sequences are reference bindings ornot and on the specifics of the bindings.

In the following, pickingT2 && would bind anrvalue to an rvalue reference. PickingT1 & wouldbind an rvalue to an lvalue reference, but the qualificationconversion toT1 is "better". Which is better?

    typedef int *      *      *const *const T1;    typedef int *const *const *const *const T2;    void foo(T1 &);    void foo(T2 &&) { }    int main() {       foo((int ****)0);       return 0;    }