On Sun, Feb 7, 2016 at 11:31 AM, Florian Weimer <f...@deneb.enyo.de> wrote: > * H. J. Lu: > >> I am proposing to update Intel386, x86-64 and IA MCU psABIs to specify >> how to pass/return empty struct: >> >> 1. "collection". A collection is a structure, union or C++ class. >> 2. "empty collection". An empty collection is: >> a. A collection without member. Or >> b. A collection with only empty collections. Or >> c. An array of empty collections. >> 3. "empty record". An empty record is Plain Old Data (POD) for the purpose >> of layout and >> a. A collection without member. Or >> b. A collection with only empty collections. >> 4. No memory slot nor register should be used to pass or return an object of >> empty collection. > > “Aggregate” may be the more standard term instead of collection.
Aggregate also include array, which is excluded here. > I think you mean “empty record” under 4. Yes. I will fix it. > Any syntactical array argument (at the C level) is should be passed as > a pointer. The language appears to change that. I didn't use aggregate so that array is excluded here. > For 2., static members and non-data members do not count. They do count here. That is why I used "POD for the purpose of layout. > Does the definition of POD vary between C++ standards? Then the > calling convention would vary as well, which is probably not what we > want. I believe that POD for the purpose of layout doesn't change between C++ standards. > How do existing C++ compilers implement empty array members (an > extension)? Does the type of such members affect whether a class is a > standard-layout class? > > Florian Are they "POD for the purpose of layout"? If yes, they are covered here. -- H.J.
