[Mesa-dev] Can we use anonymous unions?

[Connor Abbott]

On Tue, Aug 18, 2015 at 9:56 AM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> Hey,
>
> I was thinking about using an anonymous union.  Specifically, something
> like:
>
> struct shader {
>    ...
>    union {
>       struct geometry_shader_info gs;
>       struct tess_eval_shader_info tes;
>       ...
>    };
> };
>
> Are those acceptable in Mesa?  I don't think we've traditionally used
> them, but I'm not sure why.  Apparently they're part of C11, though not
> part of C99.  However, GCC allows them, presumably Clang, and it looks
> like MSVC 2005 supports them in C:
>
> https://msdn.microsoft.com/en-us/library/y9zewe0d%28v=vs.80%29.aspx
>
> We might be able to use these to avoid some of our fun
> thing->base.Base.base.program.Base.base shenanigans...
>
> --Ken
>
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Well, we already use anonymous unions in various places in NIR (for
example, the definition of nir_dest and nir_src), so they should be ok
for core Mesa. IIRC there was a problem with combining anonymous
unions and C99-style initializers, but it doesn't sound like you'll be
too worried about that.