[fpc-pascal] Extending an enumeration

[Ludo Brands]

On 28/12/2012 12:48, Mark Morgan Lloyd wrote:
> Ludo Brands wrote:
>> type
>>    TAllServerCapabilitiesBase=(uscConnected, 
>> uscCanIssueGUID,lscConnected, lscCanIssueGUID, lscIsFirebird);
>>    TUpstreamServerCapabilitiesBase= uscConnected .. uscCanIssueGUID;
>>    TLocalServerCapabilitiesBase= lscConnected..lscIsFirebird;
>>
>>    TAllServerCapabiliets=set of TAllServerCapabilitiesBase;
>>    TUpstreamServerCapabilities= set of TUpstreamServerCapabilitiesBase;
>>    TLocalServerCapabilities= set of TLocalServerCapabilitiesBase;
>
> Thanks, but I was hoping for something the other way round i.e.:
>
> type    TCommonServerCapabilitiesBase= (scConnected, scCanIssueGUID);
>
> TLocalServerCapabilitiesBase(TCommonServerCapabilitiesBase) +=
>         (lscIsFirebird); // INVALID CODE, EXAMPLE ONLY.
>
>     TLocalServerCapabilities= set of TLocalServerCapabilitiesBase;
>
> I'd be fairly happy with any solution that did the necessary 
> type/range checking at runtime.
>
Enumerations have an ordinal value that starts with 0 by default. 
"Combining" enumerations has to make sure the ordinal values are 
different. As a result you can go from bigger to smaller but not the 
other way around. In your case with 2 subranges you could do something like:

type
    TAllServerCapabilitiesBase=(uscWhatever scConnected, 
scCanIssueGUID,  lscIsFirebird);
    TUpstreamServerCapabilitiesBase= uscWhatever .. uscCanIssueGUID;
    TLocalServerCapabilitiesBase= scConnected..lscIsFirebird;

Just make sure you put the common values in the middle.

Ludo