Mutable enums

[Timon Gehr]

On 11/14/2011 01:02 AM, bearophile wrote:
> Jonathan M Davis:
>
>>> import std.algorithm;
>>> void main() {
>>>      enum a = [3, 1, 2];
>>>      enum s = sort(a);
>>>      assert(equal(a, [3, 1, 2]));
>>>      assert(equal(s, [1, 2, 3]));
>>> }
>>
>> It's not a bug. Those an manifest constants. They're copy-pasted into whatever
>> code you used them in. So,
>>
>> enum a = [3, 1, 2];
>> enum s = sort(a);
>>
>> is equivalent to
>>
>> enum a = [3, 1, 2];
>> enum s = sort([3, 1, 2]);
>
> You are right, there's no DMD bug here. Yet, it's a bit surprising to sort in-place a "constant". I have to stop thinking of them as constants. I don't like this design of enums...

It is the right design. Why should enum imply const or immutable? (or 
inout, for that matter). They are completely orthogonal.

enum Enum{
     opt1,
     opt2,
}

void main(){
     auto moo = Enum.opt1;
     moo = Enum.opt2; // who would seriously want an error here???
}


enum a = [1,2,3];

void main(){
     auto x = a;
     x = [2,1,3]; // ditto
}


>
> On the other hand this gives the error message I was looking for, until today I didn't even think about const enums:
>
> import std.algorithm;
> const enum a = [1, 2];
> void main() {
>      sort(a);
> }
>
>
> So I guess I'll start using "cont enum" and "immutable enum" instead of enums :-)
>

You can do that, but they are not a full replacement. How would you get 
a sorted version of such an enum, for instance? =)