[cxx-abi-dev] Proposed ABI changes for new C++0x SFINAE rules

[David Vandevoorde]

Attached are updated diffs for the ABI spec.  Besides a couple of minor fixes, this includes an updated treatment of parameter references in signature expressions.  There was a separate thread discussing nested function declarators, but at the recent Rapperswil meeting of WG21, an additional issue came up.  Consider:

	template<class T> auto f(T const x)->decltype(x);  // #1
	template<class T> auto f(T x)->decltype(x);        // #2

Ordinarily, top-level cv-qualifiers are ignored when forming the function type.  E.g., "int(*)(T)" and "int(*)(T const)" are the same type.  However, in expression contexts we cannot ignore the cv-qualifiers because the expression must mean the same there as it would if it appeared in the function definition (where cv-qualifiers matter).

So #1 and #2 above must be distinct templates.  Rather than encoding the cv-qualifier on the parameter type of the template signature (which would presumably be a serious break of backward compatibility), we're proposing to encode it in the reference in expression contexts (except for known non-class types in rvalue contexts, where the cv-qualifier is meaningless).  E.g., rather than encoding "decltype(x)" in #1 as "Dtfp_E" (as we'd do for #2) we use "DtfpK_E".

As usual, feedback is welcome.

Thanks,

	Daveed


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