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Re: [PATCH] rvalue reference implementation for C++0x

Mostly looks good. A few comments:

Need a space before the ( in many of the uses of TYPE_REF_IS_RVALUE and some other places.

I'd rather not expose the concept of an rvalue reference to the back end, its semantics should be encapsulated by the front end. I think the right answer is to have a wrapper for build_reference_type_* in the front end to handle the extra semantics.

I'm not sure what the best coding strategy is for this. One option would be to establish a convention of putting the rvalue ref after the non-rvalue ref in the TYPE_NEXT_REF_TO chain, or in some other field if there are others free, so that the C++ front end function can call the back end function and then use the result to look up the rvalue version.

Please quote the reference collapsing rules where you implement them in grokdeclarator and tsubst.

I'd change "valuedness" to "rvalueness" for clarity, as "valuedness" could mean "the state of having a value".

The test in compare_ics seems to check for cases where one conversion has matching rvalueness and the other doesn't, but that isn't all the rule in the working paper talks about: it also requires that for one ICS to be better than the other, the two references must differ in rvalueness, one converting to lvalue ref and the other to rvalue ref or vice versa.

In lvalue_p_1, I'd clarify the INDIRECT_REF comment by noting that the INDIRECT_REFs are just internal compiler representation, not part of the language, so we have to look through them.

Please send mail to about allocating a new type encoding for rvalue references. Since this is part of C++0x, it shouldn't be mangled using a vendor extension, it should be added to the standard ABI. Also, I'd expect it to be used instead of the "R" for an lvalue reference, not in addition.

About the deduce_ref stuff: why not just add the REFERENCE_TYPE to arg in type_unification_real rather than add another argument to unify?


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