Why is unit an alias of int in sail.h

[martinberger]

What is the rationale behind making unit an alias of int? In sail.h we find:

 typedef int unit;

I would have expected unit to be something like struct unit {}; which, I think, is used in C++.

[Alasdair]

struct unit {} is valid C++ but not valid C, as empty structs are (as far as I understand) not allowed in C, although some compilers support it as an unofficial extension.

[martinberger]

OK. Presumably typedef void unit; is also not valid C (but accepted by compilers)?

[Alasdair]

If the goal is to have a guaranteed zero-width type, I don't know of a good way to do that in standard C. I think void is a bit too special to be used here, as it's more like a thing with no size rather than a thing with zero size, and it can't really be used as a regular type. Something like enum unit {UNIT} might be the closest logically, but I think that would still end up being represented as an int with UNIT = 0.

[PeterSewell]

On Fri, 27 Oct 2023 at 20:50, Alasdair Armstrong ***@***.***> wrote: If the goal is to have a guaranteed zero-width type, I don't know of a good way to do that in standard C. I think void is a bit too special to be used here, as it's more like a thing with no size rather than a thing with zero size, and it can't really be used as a regular type. Something like enum unit {UNIT} might be the closest logically, but I think that would still end up being represented as an int with UNIT = 0.

Empty structs are not ISO C, but they are allowed in a GCC (and presumably also Clang) extension: https://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Empty-Structures.html I don't know whether there are social or technical reasons why we'd want to avoid using them for Sail->C, if there's a strong argument for them. Peter

…

— Reply to this email directly, view it on GitHub <#356 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABFMZZWG4AFSLGIFOAKAVXDYBQF65AVCNFSM6AAAAAA6SQSFZCVHI2DSMVQWIX3LMV43SRDJONRXK43TNFXW4Q3PNVWWK3TUHM3TIMBXGEZTI> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>