Re: [PATCH] build_bug.h: add wrapper for _Static_assert

[Nick Desaulniers]

On Tue, Feb 5, 2019 at 1:38 AM Rasmus Villemoes
<linux@xxxxxxxxxxxxxxxxxx> wrote:
>
> On 05/02/2019 09.05, Masahiro Yamada wrote:
> > On Mon, Feb 4, 2019 at 4:24 AM Rasmus Villemoes
> > <linux@xxxxxxxxxxxxxxxxxx> wrote:
> >> +#define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
> >> +#define __static_assert(expr, msg, ...) _Static_assert(expr, "" msg "")
> >
> > What is the "" "" for?
>
> Good point. It's a leftover from when I had a fallback-implementation of
> _Static_assert for gcc < 4.6, where I wanted to ensure that the second
> argument was a string literal, even if my fallback implementation
> ignored that argument. Now it's actually a little harmful, because

I had assumed it was for the "optional" part of the error message,
since whether you pass a string error message or not, the C
preprocessor should join them all together?

>
> foobar.c:5:34: error: expected string literal before âexpectedâ
>  static_assert(sizeof(long) == 8, expected 64 bit machine);

Hopefully you'd put `expected` in double quotes?

Note: I'm _very_ happy to see this being added.  Once it's landed, I
too can think of some places that it would work better than
BUILD_BUG_ON().
-- 
Thanks,
~Nick Desaulniers