Re: [Glsdk-devel] The use of anonymous structures

[H. H. <hen...@gm...>]

On Sun, Aug 24, 2008 at 5:14 AM, Stefanos A. <sta...@gm...> wrote:

> Την Sun, 24 Aug 2008 04:05:06 +0300,ο(η) Henri Häkkinen
> <hen...@gm...> έγραψε:
>
> > Does anyone have anything to say on this, please? I am currently working
> > hard on the GLM and I think we should resolve the issue of how we
> > actually
> > define the math types.
> >
>
> I'd go for #2 (struct/union), just slightly modified.
>
> Why use a struct? Because typing vec.x is cleaner than vec[0].
>
> Why have a union? So you can pass the struct to OpenGL without a cast.
> Compare:
>
> foo(vec.data);       // approach #2 (struct/union)
> vs
> foo((GLfloat*)vec);  // approach #3 (struct)
> vs
> foo(&vec.x);         // approach #3 (struct)
>
> To that end, it might be better to define structs like this:
>
> typedef struct GLMFoo_t
> {
>     union GLMFoo_data
>     {
>         GLfloat data[2];   // Instead of v[] or m[]
>         struct GLMFoo_fields
>         {
>             GLfloat x, y;
>         }
>     }
> } GLMFoo;
>
> This makes clear that the "data" field provides the storage for the vector
> data - v or m might be somewhat cryptic at first glance.
>

I agree that we should go with the struct-union combination. However, I have
discovered a problem:

typedef struct FOO_s {
  union {
    int di;
    struct BAS_s {
      int do;
    };
  };
} FOO;

FOO f;
f.di = 1;
f.do = 2;

This fails on GCC; f.do is not accessible (try it). I am not sure is this a
bug in GCC or is this standard conforming behaviour. So therefore, we cannot
go with the non-anonymous inner struct.

I recommend that we go with struct-union, and with anonymous inner struct,
and just use compiler #pragma (disable : warning) on Windows platform to
drop the warning it produces.

What do you think?


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-- 
Henri 'henux' Häkkinen