On Mon, Feb 8, 2016 at 12:38 PM, Richard Smith <rich...@metafoo.co.uk> wrote: > On Mon, Feb 8, 2016 at 12:05 PM, H.J. Lu <hjl.to...@gmail.com> wrote: >> >> On Mon, Feb 8, 2016 at 11:33 AM, Jonathan Wakely <jwakely....@gmail.com> >> wrote: >> > On 8 February 2016 at 19:23, Richard Smith wrote: >> >> "POD for the purpose of layout" is defined in the Itanium C++ ABI here: >> >> >> >> http://mentorembedded.github.io/cxx-abi/abi.html#definitions >> > >> > Thanks. So there's no problem using "POD for the purposes of layout", >> > and the change to "POD for the purpose of standard-layout" was >> > unnecessary and just confused things. >> >> Here is the revised proposal: >> >> 1. "class type". A class type is a structure, union or C++ class. >> 2. "empty class type". An empty class type is: >> a. A class type without member. Or >> b. A class type with only members of empty class types. Or > > > (a) is a special case of (b). > >> c. An array of empty class types. > > > It seems confusing to call an array a class type. Instead, how about: > > 2. An empty type is either an array of empty types or a class type where > every member is of empty type. > >> 3. "empty record". An empty record is Plain Old Data (POD) for the >> purposes of layout and >> a. A class type without member. Or >> b. A class type with only members of empty class types. > > > (a) is a special case of (b). > >> 4. No memory slot nor register should be used to pass or return an object >> of empty record. > > > Objects of array type are never passed or returned (but if through some > language extension they were, we'd want this rule to apply). So you don't > need rule 3 and this can be just: > > 3. No memory slot nor register should be used to pass or return an object > of empty type.
Thanks very much for your inputs. Here is the proposal: 1. "class type". A class type is a structure, union or C++ class. 2. "empty type". An empty type is either an array of empty types or a class type where every member is of empty type. 3. No memory slot nor register should be used to pass or return an object of empty type. -- H.J.
