Am Sonntag, den 16.05.2021, 16:26 +0200 schrieb Jₑₙₛ Gustedt via Liaison:
> Miguel,
>
> on Sun, 16 May 2021 16:03:05 +0200 you (Miguel Ojeda
> <miguel.ojeda.sandonis_at_gmail.com>) wrote:
>
> > On Sun, May 16, 2021 at 12:13 PM Jₑₙₛ Gustedt via Liaison
> > <liaison_at_lists.isocpp.org> wrote:
> > > Is there interest / attempt / opposition of porting this feature to
> > > C?
> >
> > Sounds good to me.
> >
> > Rust and Zig also provide it equivalent facilities, although Rust
> > provides both a safe version (panic) and an unsafe one (UB), which
> > could be worth having; and Zig provides a single one that is a panic
> > or UB depending on compilation mode.
> >
> > So a couple questions for (both) papers would be:
> >
> > - Should we have a non-UB variant that e.g. `abort()`s, like Rust?
>
> we have that already, it is called `abort`, and if we also get `defer`
> in C23 we will have `panic` ;-)
>
> More seriously, I don't think we should provide more than that,
> because if we want as specific behavior in case of violation of the
> constraint, the compiler would always do the test. But one goal of
> such a thing would be to make agressive optimizations possible.
>
> > - Should behavior depend on `NDEBUG`/`_DEBUG`/build "mode" or
> > similar, like Zig?
>
> Would the behavior then be different from `assert(false)` ?

It is maybe not ideal to convert 'assert' to 'assume' for
non-debug builds, because the code could still work when
the assertian fails bot not anymore with 'assume'.

> I think the paper talks of something very similar that could be called
> `assume(false)` and argues against it.

Maybe it is just me, but I find

assume(x);

 much clearer than

if (!x)
  __builtin_unreachable();


Martin