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From: Thiago Adams <thiago.adams@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: enum sets
Date: Thu, 29 Aug 2024 08:34:36 -0300
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On 29/08/2024 04:33, David Brown wrote:
> On 29/08/2024 01:42, Thiago Adams wrote:
>> 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.
>>
> 
> I think this could have some use-cases, but I suspect that often you 
> would want to have separate enumerations defined first, then combine 
> them with a sum type (aka variant, tagged union, discriminated type, etc.).
> 
> 
> enum monospaced_font_type {
>      cascadia
> };
> 
> enum proportional_font_type {
>      arial
> };
> 
> typedef struct {
>      enum { is_monospaced_font_type, is_proportional_font_type } tag;
>      union {
>          enum monospaced_font_type mf;
>          enum proportional_font_type pf;
>      }
> } font_type;
> 

One of my motivations was that I have a big enum and sometimes I need to 
check in switch cases all values of some type.

For instance, let's say

enum E {A, B, C, D /*until Z*/};

And I need to check a subset  for instance  A, B

To have a warning if I miss some item I need to include all cases.

void f(enum E e)
{
    switch(e)
    {
      case A:
      case B:
      break;

      case C:
      //..Z
      break;
    }
}
//warning you missing D case.


The  problem this is not practical when  the number of items is too big.
Using default:break; makes it practical but then the warning disappears.


With this enum set idea the code would be

enum E {
    enum Subset {A, B}
    ,
    C,
    D /*until Z*/
};

void f(enum Subset e)
{
    switch(e)
    {
      case A:
      break;
    } //warning you miss case  B
}