Re: Wish: scoped enum

["Arsen Arsenović" <arsen@aarsen.me>]

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Hi,

Yair Lenga via Gcc <gcc@gcc.gnu.org> writes:

> I wonder if it will be possible to add support for "scoped" enum to GCC.
> The current C standard has one name space for all enums, and different name
> space for the members of each "struct". As a result, possible to say
>
> struct foo { int a } ;
> struct bar { double a };     // This is different 'a', different type
>
> But illegal to to (ignoring the conversion to use all upper for enum).
>
> enum a { u, v } ;
> enum b { v, w } ;             // can not do this, as 'v' must be distinct
>
> One annoying side effect is that any package/module creating an enum has to
> worry about namespace collision with everyone else in the world. Common
> practices include distinct prefixes, similar to the way different libraries
> use distinct prefixes to avoid function name collision. This solution is
> far from perfect and leads to excessive long enum name.
>
> A reasonable wish list - add a magic keyword that will place the enums into
> a scope, so that the following work:
>
> SCOPED enum shirt_sz { small, medium, large } ;
> SCOPED enum shoe_sz { small, medium, medium_wide, large, xlarge } ;
>
> enum shirt_sz tshift_size = shift_sz.medium ;
> enum shoe_siz boot_size = shoe_sz.xlarge ;
>
> Not perfect, but not complex, will make enum reusable across many scenario,
> where they are currently hard to implement - because of namespace conflict
> - between system header and user headers, between different packages.
>
> A smart compiler can also alert when "types" are mixed (assign value from
> shift_sz to a variable of type shoe_sz). Not critical - as my understanding
> is that this is not enforced today. For the case that an enum symbol is
> distinct (in the current compilation unit), the compiler can allow using it
> without the namespace - practically falling back into current behavior.
>
> Feedback ? Anyone know how to get a prototype into gcc ? How one get
> approval for such "extensions".

I'd suggest, if you choose to implement this, to imitate what C++ does
for these, maybe even propose it for the standard.  There's already
established syntax and semantics.

It would certainly be nice to have such a thing in C.

Have a lovely evening.
-- 
Arsen Arsenović

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