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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.c
Subject: Re: enum sets
Date: Thu, 29 Aug 2024 01:31:40 -0000 (UTC)
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On 2024-08-29, Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
> Thiago Adams <thiago.adams@gmail.com> writes:
>> I am wondering how useful would be to have enum sets.
>>
>> Let´s say you have a function that accepts only monospaced fonts.Then
>> you can use enum monospaced_font_type. Or a switch case where you need
>> to check all and only monospaced_font_type.
>>
>> But at same type you can store at same object monospaced_font_type or
>> font_type.
>>
>> enum font_type
>> {
>>     enum monospaced_font_type
>>     {
>>         CASCADIA_FONT,
>>     },
>>     ARIAL_FONT
>> };
>>
>> This could be arranged in any way.
>
> If I understand you correctly, enum monospaced_font_type is a *subtype*
> of enum font_type.
>
> Ada has something very similar to this:
>
>     type Font_Type is (CASCADIA_FONT, ARIAL_FONT);
>     subtype monospaced_font_type is Font_type range CASCADIA_FONT .. CASCADIA_FONT;
>
> An Ada subtype is a type with an optionally added *constraint*,
> which can be checked at runtime.  But it's hard to see how you'd
> add this to C.
>
> Given your type definition, how would this behave?
>
>     void func(enum monospaced_font_type);
>     enum font_type font = ARIAL_FONT;
>     func(font);

If enums are to be "safe", the only treatment that makes sense is
a constraint violation (overridable with a cast).

The reverse conversion would not violate a constraint.

Run-time type information in enumeration tags seems like a wrong
stacking of abstractions. Enumerations are something with the help of
which you can implement dynamic typing in a run-time written in C;
you really just want them to be "dumb integers", with some compile-time
checks that catch bugs more often than they don't.

-- 
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