switch with enum

[Steven Schveighoffer via Digitalmars-d-learn]

On 11/25/15 12:17 AM, tcak wrote:
> On Wednesday, 25 November 2015 at 03:59:01 UTC, Steven Schveighoffer wrote:
>> On 11/24/15 10:51 PM, tcak wrote:
>>> I have seen a code a while ago, but even by looking at documentation, I
>>> couldn't have found anything about it.
>>>
>>> Let's say I have defined an enum;
>>>
>>> enum Status: ubyte{
>>>   Busy = 1,
>>>   Active = 2
>>> }
>>>
>>> and received a ubyte value from user.
>>>
>>> ubyte userValue;
>>>
>>> I want to switch over userValue, but that should depend on Status.
>>>
>>> switch( userValue ){
>>> ....
>>> }
>>>
>>> What I mean is that compiler should enforce values of enum "Status" to
>>> be declared in switch as it would be done with "final switch", but as
>>> you can guess, user might enter a value that is not defined by Status.
>>> Thus, I should be able to enter the case "default" as well.
>>
>> All final switch does is ensure you are covering all possible enums.
>> It assumes that the value is already a valid enum value. If you did
>> final switch on userValue, it would require you handle all 256
>> possible values for ubyte. So you would have to cast first.
>>
>>>
>>> I remember it something like switch( userValue ) with( Status ){...},
>>> but not sure about it. Maybe it was D1 code. Is there anything like this
>>> currently?
>>
>> What this does (and yes, it should work) is make it so you don't have
>> to type "Status.Busy" within your case statements. You can just type
>> "Busy". That's all.
>>
>
> As far as I see, "default" case is not allowed when final switch
> is used. From compiler developer's perspective, it is meaningful
> and I can understand, but thinking about use cases as I have
> given an example, this limitation prevents writing "tight" code.
> (That is the term I could have found to express I am trying to say).

I can see what you mean -- you want the compiler to warn that you 
haven't covered all the cases, but you don't want to have the 
expectation that the program should be in an undefined state if the 
default case is executed (currently there *is* a default case in final 
switch, which is basically assert(0)).

I think this is a worthy possibility for an enhancement -- if default 
case of a final switch is provided, then it should override automatic 
"assert(0)" default case.

-Steve