Request: nested enums

[JS]

On Tuesday, 16 July 2013 at 15:50:54 UTC, Yota wrote:
> On Monday, 15 July 2013 at 13:47:21 UTC, JS wrote:
>> Here is a better example that can actually be implemented but 
>> not pretty:
>>
>>
>>
>> final immutable struct Msg
>> {
>>    immutable int Foo = 0;
>>    immutable int Bar = 1;
>>    final immutable struct Type
>>    {
>>        immutable int Error = 10000;
>>        immutable int Ok = 10001;
>>    }
>> }
>>
>> Here type is not necessarily a logical subtype of Msg but 
>> better stated as Msg.Type.Error rather than MsgType.Error.
>>
>> If a flag distribution was used, we could do Msg.Foo || 
>> Msg.Type.Error.
>>
>> In any case generating such a structure is a bit of a pain 
>> compared to a normal enum.
>
> That could cause a bit of readability issue.  If you know Msg is
> an enum, and then see in the code Msg.Foo, Msg.Bar, and 
> Msg.Type,
> any programmer is gonna instantly assume that Msg.Type is just
> another value.  If they see Msg.Type.Error, and are still 
> certain
> that Msg is an enum, they they might reason that the enum is of 
> a
> user defined type, and you're reading the Error field/property.
> Either way, it seems a bit counterproductive.
>

I can't do anything about invalid assumptions people make. Alias 
has the exact same issue you state. If the programmer doesn't 
want to take the time to look at the code properly then it's 
their fault.

If one wants to avoid
> I do see the appeal of nesting types though, as I dislike 
> dumping
> things into the global namespace, so I might advise something
> like this:
>
> struct Msg {
> 	enum Type { Foo, Bar }
> 	enum Result { Error, OK }
> }
>
> Be careful with ORing values from different enums though, as the
> result type won't be an enum.